St. Petersburg, New York, Andrew Ellicott, Akademie der Wissenschaften, Cambridge University Press, Leonhard Euler, Shaker Verlag, Petersburg, sieve of Eratosthenes, Oxford University Press, Armagh Royal School, Royal Astronomical Society, Meriwether Lewis, Mervyn Archdall, American Astronomical Society, University of Northern Iowa, Eratosthenes, Daniel Bernoulli, President Thomas Jefferson, Thomas Jefferson, William Frederick Archdall Ellison, Verdun, Johns Hopkins University, Eulers Leute, Leonhard Eulers Leben, Petersburger Akademie der Wissenschaften, Swiss National Science Foundation, Entstehung moderner wissenschaftlicher Mechanics, Euler Committee of the Swiss Academy of Sciences, American Philosophical Society, Henry C., United States National Archives, Pennsylvania, Iowa State University, Ithaca, New York, West Point, New York, United States, John A. Garraty, solar flares, latitude observations, George Washington, the Royal Society of London, astronomical observations, Leonhard Eulers, Mervyn Ellison, Armagh Ellison, Royal Observatory, USA Ellicott, Christian Thomas Royal Astronomical Society, Armagh Observatory, Mervyn Archdall Ian Elliott Dunsink Observatory, Astronomical Society, History of Astronomy, W. de Gruyter, Ernst Paul, Ernest Benjamin, Clarendon Press, Georg Christoph, Eratosthenes von Kyrene, Helmuth Schneider, Luis Enrique, Fragmente des Eratosthenes, Luis Enrique Erro, Eratosthenes Eratosthenes, John Ericsson, Johann Strassmaier, circumference of the Earth, Suda Eratosthenes, Ericsson Erro, Alexandria, George Christoph Eimmart, Albert Einstein, Einstein, Johann Heinrich Muller, Eimmart, map of the Moon, logarithmic tables, Schriften Leonhard Eulers, Swiss Polytechnic Institute, Charles Darwin, Joachim Sandrart, phases of the Moon, Georg Eimmart, Rhete Eimmart, Eimmart Aczel, Johann Muller, Harvard University, phase of the Moon, Nuremberg Eimmart, Imperial Eimmart, Mathematical Science
Ealhwine Alcuin Easton, Cornelis Adriaan Blaauw Groningen, The Netherlands Born Dordrecht, the Netherlands, 10 September 1864 Died The Hague, The Netherlands, 3 June 1929 Dutch journalist and amateur astronomer Cornelis Easton published what seems to have been the first suggestion for the spiral structure of the Milky Way galaxy that put the center of the spiral well away from the Solar System. He was the son of J. J. Easton, a sailor, and M. W. Ridderhof and graduated from high school in 1881, next undertaking a course of instruction for people entering into government in the Dutch East Indies. Easton continued at the Sorbonne University, Paris, studying French until 1886, and after a short period of teaching, he began a career as a journalist in association with the leading Dutch newspapers Nieuwe Rotterdamsche Courant (18951906), Nieuws Adrian Blaauw: deceased.
van den Dag (19061923), and Haagsche Post (from 1923). Easton was already an enthusiastic amateur astronomer in his high school years, and he soon gained fame by his careful drawings of the brightness distribution of the Milky Way. These were published under the title La Voie Lacteґe dans l'hemisphe`re boreґal in Paris in 1893. He worked in close association with the famous astronomer Jacobus Kapteyn of the University of Groningen, the Netherlands, who highly appreciated his work, in fact so much that in 1903 the university granted Easton an honorary degree in physical sciences. Easton's best known drawing appeared in 1900 and showed a face-on view of a circular Milky Way, with the Solar System at the center of the circle, but the center of a distorted and complex system of spiral arms a considerable distance away. His next step was to incorporate star counts derived from the existing survey of the sky, the Bonner Durchmusterung, into the hypothetical structure of the galaxy. The direction of the center in this 1913 model and its structure were not confirmed by later investigations. Besides working in astronomy, Easton was active in various other fields of science, in particular climatology. In 1923, he became a member of the board of the Netherlands Meteorological Institute, and in 1928 he published an impressive statistical-historical study of the climatological conditions in Western Europe, under the title Les hivers dans l'Europe occidentale.
T. Hockey (ed.), Biographical Encyclopedia of Astronomers, DOI 10.1007/978-1-4419-9917-7, # Springer Science+Business Media New York 2014
Eckert, Wallace John
Selected References Blaauw, A. (1971). "Easton, Cornelis." In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 4, pp. 272273. New York: Charles Scribner's Sons. De Sitter, W. (1932). "The Galactic and Extra-galactic Systems." In Kosmos. Cambridge, Massachusetts: Harvard University
Press. pp. 8788 of Chap. 5. Stein, J. (July/Sept. 1929). "C. Easton in Memoriam" (in Dutch). Hemel en Dampkring. Eckert, Wallace John Robert A. Garfinkle Union City, CA, USA Born Pittsburgh, Pennsylvania, USA, 19 June 1902 Died Englewood, New Jersey, USA, 24 August 1971 American celestial mechanician Wallace Eckert pioneered the application of punch-card computing machines to problems of astronomical orbit determinations. He was the son of farmers John and Anna (Neґe Heil) Eckert, and received degrees from Oberlin College (AB: 1925), Amherst College (AM: 1926), and Yale University (Ph.D. in astronomy: 1931, with a thesis on the orbit of Trojan-type minor planet (624) Hektor, completed under Ernest Brown). From 1926 to 1940 Eckert served on the astronomy department faculty of Columbia University
, rising to the level of professor of celestial mechanics. He spent his last 2 professional years, 19681969, at Yale University, and throughout his career was particularly generous in providing computational facilities for the astronomers at Yale University working on planetary, asteroid, and satellite orbits. In 1933, Eckert worked on developing a punchcard accounting machine for astronomical calculations at the automatic scientific computing laboratory at Colombia University. The laboratory became the Thomas J. Watson Astronomical
Computing Bureau in 1937 as a joint project between the university and International Business
Machine Corporation [IBM]. The Watson Laboratory led the way in developing large-scale computers for use in World War II. In 1940, Eckert became the director of the Nautical Almanac Office of the United States Naval Observatory and served in that capacity until the end of World War II. He published his book Punch Card Methods in Scientific Computation in the same year. During the war, the Almanac Office used automatic calculation methods to develop celestial navigational charts and tables for use by the US Army and US Air Force. The first Air Almanac was published in 1940. At the end of the war, Eckert left the Nautical Almanac Office to become the director of the Watson Scientific Computing Laboratory, a department of pure science at IBM. He held this position for 23 years. The laboratory served as a major computer research and training facility in all branches of science. Hundreds of scientists were trained in scientific computation there. In early January 1948, Eckert and a team from IBM finished the Selective Sequence Electronic Calculator [SSEC], which is considered the first true electronic computer. On 27 January 1948, the SSEC became the first electronic computer to accomplish the difficult task of calculating the Moon's position. This hybrid machine was made of several systems of storage that included 12,500 vacuum tubes and 21,400 mechanical relays. Its memory section consisted of eight vacuum tubes, 150 words on a memory relay, and 66 loops of banded paper that could store 20,000 words of 20 digits each. This machine could read its instructions either from one of the paper loops or from memory. In 1954, Eckert and his team completed the Naval Ordnance Research Calculator [NORC]. At the time of its construction, NORC was the most powerful computer in the world. Eckert used SSEC and NORC to compute precise planetary positions and refine the lunar theory. In 1951, he published his book Coordinates of the Five Outer Planets. This work consisted of precise orbital calculations for the planets Jupiter, Saturn, Uranus, Neptune, and Pluto.
In the late 1950s and early 1960s, Eckert worked on developing precise positions of the Moon based on the formulas developed by astronomer and mathematician Ernest Brown. Brown's formulas consisted of about 1,650 trigonometric terms, with many of them being variable coeffi-
Bowman, John S.
(ed.) (1995). "Eckert, Wallace (John)." In The Cambridge Dictionary of American Biography, p. 213. Cambridge: Cambridge University Press. Tropp, Henry S. (1978). "Eckert, Wallace John." In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 15, pp. 128130. New York: Charles Scribner's Sons.
cients. Eckert realized that using Brown's tables
alone as a basis of improving the accuracy of
knowing the Moon's position was no longer via-
ble. He therefore developed a computer program to calculate the lunar position using Brown's for- Ecphantus
mulas directly instead of relying on tables based
on the formulas. In 1965, Eckert was able to deter- James Dye
mine that there must be a concentration of mass Northern Illinois University, DeKalb, IL, USA
near the lunar surface that was causing slight var-
iations in the Moon's orbital position. These mass
concentrations (known as mascons) were later Born Syracuse, (Sicily, Italy), circa 440 BCE
proven to exist when they caused fluctuations in
the orbital elevation of a spacecraft in lunar orbit Ecphantus is said to have identified Pythago-
as the craft passed over the mascons. Eckert's rean monads with corporeal atoms. However,
lunar positions were accurate to within a few feet so little is known of his life that some late
per century and included accounting for lunar nineteenth-century scholars doubted his exis-
oscillations as small as 1 in.
tence. Both Hippolytus and Aetius record that
In 1966, Eckert was awarded the James Craig he was a Syracusan and an atomist, so he
Watson Medal of the National Academy of must have lived when he could have
Sciences, and in 1968, he received an honorary been influenced by Leucippus and
doctorate of science from Oberlin College. Democritus. Guthrie (1962, p. 325) hazards
Eckert retired from IBM in 1967 and from his that Ecphantus "probably belonged to the last
professorship of celestial mechanics at generation of Pythagoreans who were contem-
Columbia in 1970.
poraries of Plato."
Without the pioneering computer work done In Ecphantus's version of atomism, atoms
by Eckert, his staff, and students in determining differ in size, shape, and force. They move not
the exact position of the Moon at any given time, by random and mindless physical forces, but
the manned landings on the Moon might not have by divine providence. In Democritean atomism,
been possible by the end of the 1960s. A nearside infinitely many atoms have congregated into lunar crater at 17.3 N; 58.3 E was named in infinitely many worlds scattered throughout
1973 by the International Astronomical Union to infinite space. In contrast, Ecphantus postulated
honor Wallace John Eckert, and minor planet a finite number of entities constituting a single
(1750) Eckert was named for him.
spherical cosmos with a spherical Earth at its
Contrary to common belief, Ecphantus
claimed that the Earth rotates in an easterly direction, while the sphere of fixed stars remains
Anon. (1979). "Eckert, Wallace John." In National motionless. In De Revolutionibus Nicolaus
Cyclopedia of American Biography. Vol. 58, pp. 457458. Clifton, New Jersey: James T. White and Co. Ashbrook, Joseph (1971). "A Great American Astronomer." Sky & Telescope 42, no. 4: 207.
Copernicus refers to Aetius's report of Heraclides' and Ecphantus's belief in terrestrial rotation as his inspiration for seriously considering the hypothesis that the Earth moves.
Eddington, Arthur Stanley
Selected Reference Guthrie, W. K. C. (1962). "Ecphantus." In A History of Greek Philosophy. Vol. 1, The Earlier Presocratics and the Pythagoreans, pp. 323327. Cambridge: Cambridge University Press. Eddington, Arthur Stanley Matthew Stanley1 and Virginia Trimble2 1Iowa State University, Ames, IA, USA 2University of California, Irvine School of Physical Sciences, Irvine, CA, USA Born Kendal, (Cumbria), England, 28 December 1882 Died Cambridge, England, 22 November 1944 Eddington, Arthur Stanley. Reproduced by permission of the Astronomical Society of the Pacific English theoretical astrophysicist Arthur Stanley Eddington is most widely remembered for
coordinating the 1919 solar eclipse expeditions that provided confirming evidence for the gravitational deflection of light predicted by Albert Einstein's general theory of relativity. He also formulated the modern theory of Cepheid and other pulsationally varying stars, wrote down the equations that describe how radiation moves through stellar material, and was a pioneer in attributing stellar energy sources
to "subatomic" (nuclear) processes and in recognizing that interstellar gas pervades the Milky Way Galaxy. Eddington was born to Sarah Ann Shout Eddington and Arthur Henry Eddington, a Quaker schoolmaster and the descendent of four generations of Somerset Quakers. After his father's early death, Arthur Stanley was educated at home and in small schools in Weston. His love of and talent for mathematics was soon evident, and he won many contests and prizes. At the age of 16, he won a scholarship to Owens College, Manchester, where he studied physics and math with Arthur Schuster and Horace Lamb. At Manchester, Eddington lived at Dalton Hall, where he came under the lasting influence of the Quaker mathematician J. W. Graham. Eddington was always dependent on financial support, and a Natural Sciences Scholarship allowed him to enter Trinity College, Cambridge, in 1902. There he was coached by the famous mathematician Robert Herman, and became the first second-year student to earn a place as senior wrangler on the tripos. He received his BA from Cambridge in 1905, and his MA in 1909. After teaching briefly at Trinity College, Eddington went on to become chief assistant at the Royal Observatory, Greenwich, from 1906 to 1913. In 1913, he was appointed to a fellowship at Trinity College, Cambridge, and awarded the Plumian Professorship of Astronomy and Experimental Philosophy and the directorship of the Cambridge Observatory, positions that he held until his death. The best known of Eddington's students there were theoretical astrophysicist Subrahmanyan Chandrasekhar and historian and philosopher Clive Kilmister. He advised Cecilia Payne-Gaposchkin, who had been
Eddington, Arthur Stanley
a Cambridge undergraduate, to pursue graduate energy sources; (4) endorsed the suggestion from
studies in the United States.
James Jeans, with whom he otherwise had
Eddington's early work concerned the rather little in common, that the gas in stars
motions of stars through space, based primarily would be completely ionized, so that perhaps
on proper motion data. His 1914 book, Stellar the atoms could be crammed together much
Movements and the Structure of the Universe, closer than they are on Earth; and (5) suggested
placed the Sun very near the center of the stellar an approximation to the structure of stellar
system (then called the Universe, now called the atmospheres (the Milne-Eddington approxima-
Galaxy) and endorsed the two-stream hypothesis tion) in which the particles that produce
of Jacobus Kapteyn, in which the motions the continuum ("rainbow") and those that pro-
were described by two intermingling streams of duce the absorption lines are completely
stars moving in different directions relative to the mixed. The opposite, with the absorption layer
Sun. The description given by Karl on top, is the Schuster-Schwarzschild approxima-
Schwarzschild in terms of velocity ellipsoids tion, due to his former teacher and German
turned out to be more useful. Both were incom- contemporary.
plete descriptions of the effects of a differentially During World War I, Eddington became
rotating galactic disk, a nonrotating halo, and embroiled in controversy within the British
a solar position far from the center.
astronomical and scientific communities. Many
In Cambridge, Eddington turned his attention astronomers, chief among them Herbert
to the interior structure of stars, how energy was Turner, argued that scientific relations with all
transported from the center to the photosphere, of the Central Powers should be permanently
and what the sources of that energy might ended due to their conduct in the war. Eddington,
be. Robert Emden had formulated the mathe- a Quaker pacifist, struggled to keep wartime
matics of stars in which energy was carried by bitterness out of astronomy. He repeatedly called
convection, and Schwarzschild had begun con- for British scientists to preserve their prewar
sidering the effects of radiation shortly before his friendships and collegiality with German
death in 1916. Eddington's standard model, scientists. Eddington's pacifism caused severe
begun in 1916, was a completely radiative star, difficulties during the war, especially when he
and he concluded that the most common kind of was called up for conscription in 1918. He
stars, like the Sun, were the ones where the claimed conscientious objector status, a position
pressure due to the hot gas and the pressure due recognized by the law, if somewhat despised by
to radiation were equal. He, like most contempo- the public. However, the conscription board
raries, thought that stellar composition must be refused to grant such status since he had
similar to that of the Earth, with lots of silicon, previously held a deferment for his astronomical
oxygen, and iron.
work; the government would not allow him
During this period, Eddington (1) correctly to be both a scientist and a Quaker. Only the
described the variable brightness of Cepheids as timely intervention of the Astronomer Royal
being due to inward and outward pulsation of the and other high-profile figures kept Eddington
stars, driven by ionization and recombination of out of prison.
gas just under their visible surfaces; (2) coined During the war, Eddington was Secretary of
the term "main sequence" to describe the locus of the Royal Astronomical Society (RAS), which
the majority of stars in a Hertzsprung-Russell meant he was the first to receive a series of letters
diagram and the word "bolometry" to describe and papers from Wilhelm de Sitter regarding
measuring the brightness of stars at all wave- Einstein's theory of general relativity. Eddington
lengths; (3) derived for the first time the relation- was fortunate, being one of the few scientists able ship between luminosity and mass (L / M 3) for to understand the mathematics of relativity, and
fully radiative stars, which agrees with observa- also one of the few interested in pursuing a theory
tions and does not depend on the nature of the developed by a German physicist. He quickly
Eddington, Arthur Stanley
became the chief supporter and expositor of relativity in Britain. Eddington and Astronomer Royal Frank Dyson (one of the few other internationalists in the RAS) organized the 1919 expedition to make the first empirical test of Einstein's theory: the measurement of the deflection of light by the Sun's gravitational field. In fact, it was Dyson's argument for the indispensability of Eddington's expertise in this test that allowed him to escape incarceration during the war. The eclipse expedition to Principe in Africa and Sobral in Brazil was held up as a complete success, and Eddington embarked on a campaign to popularize relativity and the expedition as landmarks both in scientific development and in international scientific relations. In recent years, Eddington has been accused of having manipulated the data from the expedition to favor Einstein, but there is no evidence that this was the case. During the 1920s and 1930s, Eddington gave innumerable lectures, interviews, and radio broadcasts on relativity (in addition to his textbook mathematical theory
of Relativity), and later, on quantum mechanics. Many of these were gathered into books, including Nature of the Physical World and New Pathways in Science. They were immensely popular with the public, not only because of Eddington's clear exposition, but also for his willingness to discuss the philosophical and religious implications of the new physics. He argued for a deeply rooted philosophical harmony between scientific investigation and religious mysticism, and also that the positivist nature of modern physics (i.e., relativity and quantum physics) provided new room for personal religious experience. Unlike many other spiritual scientists, Eddington rejected the idea that science could provide proof of religious propositions. His popular writings made him, quite literally, a household name in Great Britain between the world wars. In addition to receiving popular acclaim, Eddington also received most of the traditional professional accolades, including more than a dozen honorary doctorates, memberships, and medals of the Royal Society (London), the RAS
(which he served as president and which later named one of its medals for him), the United States National Academy of Sciences
, and the Astronomical Society of the Pacific. By the time of the 1926 publication of his Internal Constitution of the Stars, Eddington had taken definite stands on a number of other issues. One was the basic source of stellar energy, which he attributed to processes concentrated at the centers of stars that would change one element into another. This allows for stellar lifetimes much longer than the gravitational contraction timescale of William Thomson and Hermann Helmholtz but much shorter than the 10121013 years advocated by Jeans on dynamical grounds, which would have required the complete annihilation of stellar matter. He also applied general relativity to white dwarf stars, predicting that they should display a gravitational redshift (reported the next year, 1925, by Walter Adams). On the other hand, Eddington accepted Ralph Fowler's 1926 suggestion that white dwarfs would be fully degenerate, but rejected the later conclusion of his student Chandrasekhar that there was an upper limit to the possible masses of these stars. Eddington's dispute with Chandrasekhar was not based on racism, as is sometimes claimed, but rather on straightforward disagreements about how to best combine relativity with quantum mechanics. Eddington was also involved in applying general relativity to expanding universe models. He supported Georges Lematre's 1927 work, but rejected the idea of a discontinuous "Big Bang" beginning to the Universe. His own work in cosmology focused on the role of the cosmological constant, which most scientists had rejected as superfluous. From about 1900 to 1930, the astronomical community was divided over whether diffuse material was pervasive in interstellar space, whether it might absorb significant amounts of light, and whether accretion from diffuse material might significantly augment the masses and brightnesses of stars. Eddington correctly interpreted observations by John Plaskett as meaning that at least calcium and sodium were
Edgeworth, Kenneth Essex
pervasive, although he did not think such material
would result in significant absorption or Edgeworth, Kenneth Essex
Toward the end of his life, Eddington Steven J. Dick
attempted his own unification of general relativ- NASA/LIBRARY OF CONGRESS
ity and quantum mechanics in the posthumously DC, USA
published Fundamental Theory. He provided
what were intended as calculations from first
principles of the total number of particles in the Born Streete, County Westmeath, Ireland,
observable universe, of the fine structure constant 26 February 1880
of atomic physics, and other basic properties of Died Dublin, Ireland, 10 October 1972
nature. Few of his colleagues attempted, or were
able, to follow the arguments, some of which Kenneth Edgeworth was an Irish astronomer,
were heavily philosophical.
economist, and engineer, best known in astron-
omy for his proposal that a reservoir of icy bodies
exists beyond Neptune. Beginning in the early
1990s, a reservoir of such objects was indeed discovered and is sometimes known as the
Douglas, Allie V. (1956). The Life of Arthur Stanley Edgeworth-Kuiper belt (though more often in Eddington. London: Nelson. (There has been little the United States simply as the Kuiper Belt).
critical scholarship written on Eddington. The best biographical work on Eddington remains this uneven treatment.) Eddington, Arthur S. (1914). Stellar Movements and the Structure of the Universe. London: Macmillan.
Edgeworth also published in the fields of star formation and the origin and development of the Solar System. Asteroid (3487) Edgeworth is named in his honor.
(Representative of his work in statistical cosmology.) -- (1920). Space, Time and Gravitation. Cambridge: University Press. -- (1923). Mathematical Theory of Relativity. Cam- bridge: University Press.
Edgeworth was the son of Thomas Newcomen Edgeworth (18501931) and Elizabeth (Wilson, died 1929) Dupreґ. His career was not typical for that of an astronomer. His interest in astronomy
-- (1926). The Internal Constitution of the Stars. Cambridge: University Press. (Representative of his work in stellar structure.) -- (1928). Nature of the Physical World. Cambridge: University Press.
may have originated with his uncle, William E. Wilson, who had established an observatory with Grubb 12 and 24 in. reflectors at the house where Edgeworth was born. But in 1897,
-- (1933). The Expanding Universe. New York: Macmillan. (A good introduction to his views on relativistic cosmology.) Graham, Loren (1981). Between Science and Values. New York: Columbia University Press. (Discussion of
at age 17, Edgeworth joined the Royal Military Academy and was commissioned in the Royal Engineers the following year. He joined the School of Military Engineering at Chatham
Eddington's popular, philosophical, and religious writings.) Hufbauer, Karl (1981). "Astronomers Take Up the Stellar-Energy Problem, 19171920." Historical Studies in the Physical Sciences 11: 277303.
before transferring to South Africa
2 years later. Edgeworth served during World War I as the head of a signals unit, setting up communication lines in France. He continued his signals
(The best treatment of Eddington's work in stellar astrophysics.) Paul, Erich Robert (1993). The Milky Way Galaxy and Statistical Cosmology, 18901924. Cambridge: Cambridge University Press. (Deals with the statistical
work after the War and was promoted to the rank of Lieutenant Colonel. Meanwhile, in 1917 Edgeworth had married Isabel Mary (Pigott) Eves, and in 1926 together they traveled to
cosmology in Eddington's relativistic cosmology.) Stanley, Matthew (2003). "`An Expedition to Heal the Wounds of War': The 1919 Eclipse and Eddington as Quaker Adventurer." Isis 94: 5789. (A thorough treatment of the 1919 eclipse expedition.)
Khartoum, where he became the chief engineer in the Sudanese Department of Post and Telegraphs. Here he designed and distributed wireless transmitters, among other duties.
Edgeworth, Kenneth Essex
In 1931 Edgeworth returned to Ireland and resided at Cherbury, Booterstown, County Dublin, his parents' final home, where he lived until his death 41 years later at the age of 92. During the 1930s, in the midst of the Great Depression, Edgeworth studied international economics and published four books on the subject. Aside from a commentary on two papers by Raymond Lyttleton on the fission of rotating bodies, published in 1939, Edgeworth's earliest and best-known astronomical work dealt with the possibility of Trans-Neptunian objects. Both Edgeworth and the American astronomer Gerard Kuiper noted in the 1940s and 1950s that there was no reason to expect the Solar System to end with Neptune or Pluto. Quite aside from possible major planets, Edgeworth theorized in a paper published in 1943, shortened because of the scarcity of paper during World War II, that comets might originate in a reservoir beyond Pluto. He made this suggestion in the context of the evolution of our planetary system, part of his larger cosmogony in which galaxies, stars, planetary systems, planets, and satellites were all evolving. In short it was part of what we could today call cosmic evolution, in which the evolution of forms is only a part of the evolutionary relationship among forms and the larger evolution of the Universe itself. Edgeworth's suggestion was made in a single qualitative paragraph on "The Comets," in which he proposed that the cloud that condensed into the Solar System must have extended to greater distances than Pluto and that the condensations in the outer regions did not condense into planets, but "retained their individuality," leaving the outer regions of the Solar System "occupied by a very large number of comparatively small bodies." In contrast to the asteroids, he surmised, these comets would be "astronomical heaps of gravel without any cohesion." A single sentence following this paragraph suggested these objects occasionally wander to the inner Solar System and are seen as comets. The same points were elaborated, again as a small part of a much larger paper but this time more quantitatively, in 1949.
In 1951 Kuiper also independently argued that such objects would be scattered to the Oort Cloud and perturbed back into the inner Solar System as comets. Harvard astronomer Fred Whipple and others developed these ideas in the 1960s, and by 1980 a comet belt was advanced as the source of short-period comets, as was the Oort Cloud for long-period comets. The short-period belt was first named the "Kuiper belt" in 1988, and that term, or the alternative "EdgeworthKuiper Belt," gained rapid usage thereafter. The question of which is the better nomenclature remains open, and such controversies are not uncommon in astronomy. Detection of any such objects, however, remained elusive, since a given asteroid was 10,000 times fainter when moved from 3 to 30 astronomical units. All this changed with the arrival of CCD technology in the 1990s, which enabled detection of extremely faint objects now recognized as Edgeworth-Kuiper Belt Objects, along with a few possible inner Oort Cloud members. The first such objects were reported by David Jewitt and Janet Luu in 1993. Many hundreds are now known. Edgeworth's book, The Earth, the Planets and the Stars: Their Birth and Evolution, published in 1961, was a summation of much of his work, again making his points in the context of a larger evolutionary scheme. Edgeworth was elected a fellow of the Royal Astronomical Society, a member of the British Astronomical Association in 1943, and a member of the Royal Irish Academy in 1948. He also held membership in the Institution of Electrical Engineers. His eclectic career is summed up in the title of his autobiography, Jack of All Trades: The Story of My Life (1965). Acknowledgments This biography draws substantially from the work of McFarland (1996), gratefully acknowledged. Selected References Edgeworth, Kenneth E., "The Evolution of our Planetary System," JBAS, 53, (1943), 181188. Edgeworth, Kenneth E., "The origin and evolution of the solar system," MNRAS, 109 (1949), 600609.
Edgeworth, Kenneth E. The Earth, the Planets and the Stars: Their Birth and Evolution (London: Chapman and Hall, 1961). Edgeworth, Kenneth E. Jack of All Trades: The Story of My Life (Dublin: Alan Figges, 1965).
Wolf-Rayet stars, whose spectra had been something of a mystery since their discovery in the nineteenth century. After obtaining his degree, Edleґn remained at
McFarland, J., "Kenneth Essex Edgeworth--Victorian Polymath and Founder of the Kuiper Belt?" Vistas in Astronomy, 40 (1996), 343354; on 343.
Uppsala as a docent, finally being appointed to the professorship of physics at the University of Lund in 1944, a chair previously held by spectroscopists Anders A° ngstroЁm and
Johannes Rydberg. Edleґn continued to work
Edleґ n, Bengt
on atomic spectra, focusing on the similarities of
atoms that have the same numbers of electrons,
Roy H. Garstang University of Colorado, Boulder, CO, USA
following ionization. (For instance, singly ionized magnesium is like sodium, and singly ionized argon like chlorine.) He took a suggestion
from Walter Grotrian to follow such
Born Ringarum, OЁ stergoЁtland, Sweden, 2 November 1906 Died Lund, Sweden, 10 February 1993 Swedish spectroscopist Bengt Edleґn solved a 70-year-old puzzle by identifying emission lines in the solar corona (discovered in 1869 by Thomas Young) with transitions in very highly ionized atoms, thereby demonstrating that the corona is much hotter than the visible surface of the Sun. He received his secondary education in NorrkoЁping, Sweden, and entered the University of Uppsala in 1926, earning a series of degrees ending with a doctorate in 1934. By 1925, optical spectroscopy had reached a shortest wavelength of 155 A° , while X-ray spectroscopy had reached a longest wavelength of 17 A° . Karl M. G. ("Manne") Siegbahn of Uppsala, who had received the 1924 Nobel Prize in Physics for his work on X-ray spectroscopy, suggested that Edleґn should try to fill in the gap. This led to a doctoral thesis on the ultraviolet spectra of light elements from lithium to oxygen, with wavelength measurements and identifications of energy levels extending up to carbon and nitrogen with four electrons removed and oxygen with five electrons missing. This early work led to the 1932 identification of emission lines of ionized carbon, nitrogen, and oxygen in
sequences right on up to very highly ionized atoms of argon, calcium, iron, and nickel, allowing him to predict the wavelengths that these atoms should emit or absorb. A very important result was that a line at 5,303 A° would be produced by iron deprived of 13 electrons. This wavelength corresponded to a green emission feature seen in the spectrum of the solar corona during eclipses since 1869 and sometimes attributed to a nonexistent new element called "coronium." In 1942, Edleґn identified this and a number of other coronal lines. Because of wartime barriers to transatlantic communication, the news first reached the United States the following year in a paper written by Belgian astronomer Polydore Swings. At Lund, Edleґn established a large group of spectroscopists to work on other elements in other ionization states. The lines they predicted very often turned out to occur in the spectra of stars, gaseous nebulae, and even quasars, and the identifications made it possible to use these lines to determine the compositions and temperatures of the astronomical objects. Other features, like a pair of lines due to carbon missing three electrons, proved to be signatures of hot gas flowing away from stars in massive winds. The beginning of ultraviolet astronomy from satellites in the 1970s revealed many more of Edleґn's lines, just as he was reaching emeritus status in 1973. Nonetheless, he continued to be an active member of
the community for a number of years beyond
Roy H. Garstang died in 2009.
Eggen, Olin Jeuck
Among the honors Edleґn received for his work were medals and prizes from the Royal Astronomical Society, the Optical Society of America, and the United States National Academy of Sciences. Selected References Anon. (1975). "P. F. Klinkenberg and B. Edleґn of the University of Lund, and R. Garstang of JILA, participants in the July 1974 International, Conference on Atomic Physics held in Heidelberg." Applied Optics 14: 2601. (Meeting photo.) Hufbauer, K. (1993). "Breakthrough on the Periphery: Bengt Edleґn and the Identification of Coronal Lines, 19391945." In Center on the Periphery: Historical Aspects of 20th-Century Swedish Physics, edited by Svante Lundqvist, pp. 199237. Canton, Massachusetts, Science History Publications. Milne, E. A. (1945). "Address Delivered by the President, Professor E. A. Milne, on the Award of the Gold Medal to Professor Bengt Edleґn." Monthly Notices of the Royal Astronomical Society 105: 138145. Persson, W. and I. Martinson (1994). Physica Scripta T31: 5. Eggen, Olin Jeuck Virginia Trimble University of California, Irvine School of Physical Sciences, Irvine, CA, USA Born Rock County, Wisconsin, USA, 9 July 1919 Died Canberra, Australia, 2 October 1998 Olin J. Eggen observed the stars from at least five continents but is best remembered for his contribution to a heavily theoretical paper, written with Donald Lynden-Bell and Allan Sandage, in 1962. It put forward a model for the formation and evolution of spiral galaxies like the Milky Way that begins with a very extended, nearly spherical cloud of gas. As the cloud contracts under its own gravitational force, some of the gas forms stars, which eject heavy
elements made by nuclear reactions in them, while the rest of the gas gradually spins up (conserving angular momentum) to end up in a flat, rotating disk. This monolithic picture accounted for the observed correlations of stellar ages, dynamics, and chemical composition
s. Old, metal poor (Population II) stars are in a nearly spherical halo, moving randomly like the molecules of a gas, while young, metal-rich stars (Population I) and the residual gas are in a thin, rotating disk. The model has since been largely superseded by a hierarchical picture, with big galaxies built out of mergers of smaller ones, but the Milky Way nevertheless looks quite a lot like Eggen, Lynden-Bell, and Sandage said it should. Eggen was the eldest of three children of a Norwegian father and a German-American mother, born on a farm. He grew up in Orfordville, Wisconsin, and worked his way through to a BA at the University of Wisconsin, tending bar and playing the piano in nightclubs. He also learned to interact with politicians, a skill useful in his later career as an observatory director. Following civilian service with the United States military, he returned to the University of Wisconsin, earning a 1948 Ph.D. under Joel Stebbins, though most of his work in photometry and radial velocity measurements was guided by Albert Whitford. The thesis dealt with Algol, a peculiar eclipsing binary, which he thought might have four component stars, and 44 iota Bootes, a triple. Eggen's subsequent career was a somewhat peripatetic one: Lick Observatory (19481956), Royal Greenwich Observatory (19561961), California Institute of Technology and Mount Wilson and Palomar Observatories (19611966), Mount Stromlo Observatory, (19661977), and Cerro Tololo Inter-American Observatory (19771998), though he returned frequently to Australia in his later years. He had intermittent administrative responsibilities at Greenwich and Cerro Tololo and was director at Stromlo during the period when plans and designs for what eventually became the AngloAustralian Telescope and Observatory were
Eggen, Olin Jeuck
being formulated, with considerable difficulty. weather. Much of his time in Australia and
Eggen left after severe disagreement with other Chile went to trying to establish moving groups
members of the governing board about how of stars. A given group could include stars of
things ought to be done. Indeed, all his depar- different ages and compositions and might not
tures, except that from Mount Wilson, seem to even be very compact in space; but the stars, he
have been at least a bit stormy. On leaving Green- said, shared three-dimensional motion. Later
wich he took with him a file of papers pertaining very large surveys by others (especially the
to the discovery of Neptune, apparently intending Sloan Digital Sky Survey) have found similar-
to write a book on the topic. The file was recov- sounding star streams further away from us in the
ered only after his death.
galactic halo. These are interpreted as relics of
Both the Eggen, Lynden-Bell, and Sandage small galaxies captured by the Milky Way and
paper and Eggen's next most enduring contribu- torn apart tidally. Such streams are part of the
tion belong to the Pasadena period. This was evidence for a hierarchical model of galaxy for-
collaboration with Jesse Greenstein that mation and evolution, and in light of them,
expanded the known inventory of white dwarfs Eggen's moving groups might well repay serious
from a few dozen to hundreds and provided reexamination. It would be ironic if he had, in
the foundation for later astronomy of stars fact, found early evidence for the model opposed
below the main sequence. Much of his work to the monolithic Eggen, Lynden-Bell, and
before and after that period aroused skepticism, Sandage one.
which undoubtedly contributed to friction with Eggen himself, in 1993, described his per-
sonal life (perhaps except for that during the
While at Lick, Eggen plotted color-magnitude war) as uninteresting and not worth discussing.
diagrams for a number of clusters, using his own He married the widow of a wartime friend and
observations, in a set of wavelength bands that, adopted her two children in 1952, but the mar-
although recommended by other distinguished riage was over in a few years. Among his
colleagues, turned out to be a poor choice. honors were the Russell Lectureship of the
Because the blue color included both sides of American Astronomical Society in 1985,
the wavelength that ionize hydrogen, it was not a vice-presidency of the Royal Astronomical
a good luminosity indicator. This, plus excessive Society (19611962), the presidency of the
optimism, was apparently responsible for Eggen Australian Society of Astronomers
finding a great deal of structure in these diagrams (19711972), and a life membership in the
that no one else, using more suitable colors, could Astronomical Society of the Pacific. He was
reproduce. His papers from around 1950 collec- elected to the International Astronomical
tively reported five pieces to the main sequence, Union, but resigned in 1970.
each with a dozen or so stars falling very pre-
cisely on one of five curved (and sometimes
intersecting) "trend lines." He thought that the Selected References sequences were correlated with rotation, mag-
netic fields, mass and spectral type of compan- Becker, W. 1952. IAU Transactions VIII, 361 (color ions, and widths of the hydrogen lines, but systems).
never in any systematic way that might have evolutionary implications. Indeed the papers make no mention of stellar evolution, whose outlines were just then being established by
Eggen, O.J. 1948. ApJ 108, 1 & 15 (thesis). Eggen, O.J. 1951. ApJ 113, 657 (trend lines). Eggen, O.J. 1993. ARA & A 31, 1 (autobiography, sort of). Eggen, O.J. 1996. AJ 112, 1575 (moving groups).
others. Eggen was an indefatigable observer and a prolific author, preferring telescopes small even for his time and only the most perfect
Eggen, O.J. & Greenstein, J.L. 1965. ApJ 145, 63. Eggen, O.J., Lynden-Bell, D. & Sandage, A 1962. ApJ 136, 748. Freeman, K.C. 2000. Astronomy & Geophysics 41.1, p. 36.
Gregory, Jane. 2007. Fred Hoyle's Universe (a different view of the early days of the AAT; there is also a Hoyle biography by S. Mitton). Johnson, H.L & Morgan, W.W. 1951. ApJ 114, 522 (color systems, particularly the ones Eggen used and their problems). Kron, G. R. 1998. Telephone conversation with author. Rawlins, D. 1999. DIO 9.1, 3 (the Neptune papers). Trimble, V. 2000. Unpublished extended obituary of OJE, excerpted and heavily edited in PASP 113, 131135). Eichstad, Lorenz Jurgen Hamel Universitat Landau, Landau in der Pfalz, Rheinland-Pfalz, Germany Alternate Name Laurentius Eichstadius Born Stettin (Szczecin, Poland), 1596 Died Danzig (Gdanґ sk, Poland), 1660 Laurentius Eichstadius was an astrologer and ephemeris writer. Only a little is known about the life of Eichstadius. In his works, he declared himself to be not only a doctor of medicine, an ordinary civic health officer in the city of Szczecin in Pomerania (then German), but also an Iatro Physicus, a doctor involved in astrology. For an unknown length of time, Eichstad was professor of medicine and mathematics in Danzig. Eichstad's initial shorter writings began to appear in 1622 and involved astrological subjects: the great conjunctions between Jupiter and Saturn along with their astrological consequences, astrometeorological forecasts for 16301633, and a defense of astrology against the reproach of being a form of forbidden magic, an issue that was frequently discussed at the time. If these brief works had not stood out from the published masses of astrological material, Eichstad's ephemerides would have
obtained more prominence and even enjoyed widespread popularity. The tables appeared in three volumes: Vol. 1 for 16361640, Vol. 2 for 16411650, and Vol. 3 for 16511665. For each day of the respective years, they indicated the position of the Sun, the Moon, and the planets; the time of their rising and setting; the phase of the Moon; etc. In addition, the calculations of the Sun, Moon, and their eclipses were based on Tycho Brahe's planetary theory as revised by Christian Severin (Longomontanus; Astronomia Danica, 1622), while the calculations for the planets were grounded in the Rudolphine Tables of Johannes Kepler. Ephemerides were of great importance because they were used to cast horoscopes and to construct the popular astronomical-astrological calendars. In the first volume, Eichstad dealt with the history of ephemerides beginning with Johann Muller (Regiomontanus), provided several examples of the uses of an ephemeris, and included star catalogs for 1,600 and 1,700, formulated according to Brahe's precession constant of 5100/year, as well as a record of the rising and setting of stars on the latitude of Szczecin (53 300 N). The second volume contains, after an explanation of logarithmic calculations, a number of logarithmic tables based on the one composed by John Napier. In the third volume, 100 aphorisms about astrology are stated. The tables upon which ephemeris calculations were based (rising of the signs of the zodiac, conversion tables for the sexagesimal systems, tables of the Sun's motion, precession, the precise rising of each degree of the zodiac, and tables for calculating the Moon's movement and deviant movement) were published by Eichstad in 1644 as Tabulae harmonicae coelestium motuum. Selected Reference Eichstad, Lorenz (16341644): Pars prima ephemeridum novarum coelestium [et pars altera et tertia, for 16361660]. Stettin: Rhete
Eimmart, Georg Christoph
commissioned, for example, from the Nuremberg
Eimmart, Georg Christoph
mechanic Johann Ludtring a planetarium (orrery)
with a diameter of approximately half a meter to
demonstrate the workings of the Copernican
Universitat Bern, Bern, Switzerland
system. On the pylons of the observatory
alongside the instruments for measuring angles
were also telescopes.
Born Regensburg, (Bavaria, Germany),
From 1678 Eimmart observed and
22 August 1638
investigated the zodiacal light. In 1679 he
Died Nuremberg, (Germany), 5 January 1705 determined the local magnetic declination.
Through a pendulum experiment he was able to
Georg Eimmart was an observational astronomer, derive a proof of the rotation of the Earth.
instrument-maker, and copper engraver. He was Detailed observations remain of eclipses, comets,
the son of George Christoph Eimmart, a painter and the Moon. Simultaneously with
and copper engraver, and Christiana Bauss. Christiaan Huygens, Eimmart established
Eimmart was first apprenticed to his father as the diurnal period of the refraction of starlight
a painter and then trained in copper engraving through the Earth's atmosphere. In 1694 he pro-
and etching with Joachim Sandrart. From 1654 duced a map of the Moon that was published in
he studied mathematics, astronomy, and jurispru- Johann Zahn's Specula Physico-mathematico-
dence at the University of Jena. Following the historica. Subsequently, the publisher of terres-
death of his father in 1658, Eimmart returned to trial maps, Johann-Baptist Homann, published
Regensburg, then proceeded to Nuremberg in a map of the heavens by Eimmart. Eimmart also
1660, where he became codirector, alongside produced celestial and terrestrial globes. His sci-
Sandrart, of the Nuremberg School of Painting entific archive, which was used by many of his
from 1674, and sole director from 1699 to 1704. students, was lodged first with his son-in-law
Eimmart worked mainly as copper engraver and Muller in Altdorf; then, after several sojourns,
etcher, but was not so prominent as a painter. the 56 volumes eventually came to the Imperial
Eimmart married Anna Walther in 1668. Their Public Library in Saint Petersburg, now the
daughter, Maria Klara, later married professor Russian National Library.
Johann Heinrich Muller in Altdorf in 1706 and A lunar crater is named Eimmart (24.0 N,
died during childbirth in the following year.
In 1677 Eimmart established a private obser- A number of Eimmart's manuscripts may be
vatory near the castle in Nuremberg. Its operation found in the Royal Society of London.
was interrupted in 1688 by the threat of war with
France. In 1691 the observatory was Acknowledgments Translated by Peter Nockolds.
reestablished, and continued to function until
1757. Eimmart instructed many young people in
observation. His daughter Maria Klara supported Selected References
him in his astronomical work. She produced
250 drawings of the phases of the Moon as well as the work Iconographia nova contemplacionum de Sole. Eimmart was both builder and developer of various astronomical measuring-instruments, above all devices for measuring angles (sextants, quadrants, etc.). He used astronomical clocks and developed a helioscope. Eimmart
Aczel, Amir D. (2003). Pendulum: Leґon Foucault and the Triumph of Science. New York: Atria Books. Imhoff, Christoph von (1989). Beruhmte Nurnberger aus neun Jahrhunderten. 2nd ed. Nuremberg: A. Hofmann. Pilz, Kurt (1977). 600 Jahre Astronomie in Nurnberg. Nuremberg: Carl. Poggendorff, J. C. (1863). "Eimmart." In Biographischliterarisches HandwoЁrterbuch. Vol. 1, col. 651. Leipzig.
Whitaker, Ewen A. (1999). Mapping and Naming the
Moon: A History of Lunar Cartography and
Wibner, Adolf (1959). "Eimmart, Georg Christoph."
In Neue deutsche Biographie. Vol. 4, p. 394. Berlin:
Duncker and Humblot.
Einhard Thomas Hockey Department of Earth Science, University of Northern Iowa, Cedar Falls, IA, USA Born Maingau, (near Frankfort), circa 770 Died Seligenstadt, Hessen, (Germany), 14 March 840 Charlemagne's biographer Einhard recorded the first Western report of a sunspot since (possibly) Theophrastus. The event probably occurred between 17 and 24 March 807 and was thought at the time to be a transit of Mercury. Selected References Schove, D. Justin (ed.) (1983). Sunspot Cycles. Stroudsburg, Pennsylvania: Hutchinson Ross Publishing Co. Vaquero, J. M. and Vaґzquez, M. (2009). The Sun Recorded Through History (Astrophysics and Space Science Library, Vol. 361). New York: Springer. Einstein, Albert Gerald Holton Department of Physics, Harvard University, Cambridge, MA, USA Born Ulm, (Baden-Wurttemberg), Germany, 14 March 1879 Died Princeton, New Jersey, USA, 18 April 1955
Albert Einstein, who transformed and advanced science as only Isaac Newton
and Charles Darwin had done, was the son of Hermann and Pauline (neґe Koch) Einstein. Einstein's father operated an electrotechnical business but with limited success. During his lifetime, Einstein published, in addition to several books, over 300 scientific articles, many of which are, to this day, the basis of spectacular new advances. Einstein's contributions spanned a great variety of fields. These include the special relativity theory [SRT] that revised our notions of space and time; brought together under one view electricity, magnetism, and mechanics; dismissed the nineteenth-century concept of ether; and revealed as a by-product the equivalence of mass and energy (E ј mc2). In those first decades of work, Einstein also successfully applied statistical mechanics to explain Brownian motion; proposed a theory that the energy carried by a light wave is quantized (E ј hn), thereby explaining the photoelectric effect (for which he was awarded the Nobel Prize for Physics in 1922); and made contributions to the quantum theory of specific heats, and the concept of stimulated emission
, which became a parent of laser physics. Within months of his birth, Einstein's family had moved from Ulm to Munich. Entering its Luitpold Gymnasium in 1888, he found the school to favor a militaristic style of instruction that he found repugnant. Thus, Einstein resorted to his lifelong passion for self-education. Among those readings that proved influential were, at age 12, a book on Euclidean plane geometry, and popular books on science by Aaron Bernstein and Ludwig Buchner, along with Alexander von Humboldt's Cosmos, and (reportedly) Charles Darwin's Origin of Species. At age 13 and again at 16, he read Immanuel Kant's Critique of Pure Reason. From childhood on, Einstein was exposed to, and became fascinated with, the classics of literature and of music. In 1894, though 2 years younger than the usual age for entry, Einstein tried to be admitted to the Swiss Polytechnic Institute in Zurich. On failing the entrance examinations (although doing well in physics and mathematics), he entered the Cantonal (Secondary) School in Aarau, Switzerland,
where the youngster blossomed in a friendly, sup- Starting in 1907 and coming to a climax in
1915/1916, Einstein developed, in intense labor,
In 1896, Einstein entered the polytechnic to the general relativity theory [GRT], which can be
obtain a diploma for high-school teaching, but considered a reinterpretation of gravitation as
also took courses on Kant and Goethe. One of the effect of a curvature of space-time. His his classmates was Mileva Maric0, from southern long-hoped-for (but never achieved) unified
Hungaria. An early romance and intellectual field theory was to embrace the geometrization
kinship resulted in their marriage in January of electromagnetic field
s. Einstein attempted
1903. The couple had two sons, Hans Albert to achieve the stability of a spatially bounded
and Eduard and a somewhat mysterious daughter, Universe by including a "cosmological constant"
born before they were married, who apparently (later retracted) and gravitational waves; he also
died quite young. Over time, with Einstein's calculated that the gravitational fields of astro-
growing fame pulling him away, and Mileva's nomical objects could act as "lenses" to create
earlier moodiness reportedly turning into images of objects located far beyond them. Early
schizophrenia (which also came to afflict her successes of the GRT included explaining the
sister and younger son), the marriage dissolved degree of deflection of starlight passing close to
into unhappiness. Their divorce became final in the Sun (observed in 1919 during a total solar
1919, whereupon Einstein married his cousin, eclipse), the "red shift" of light moving through
a gravitational field, and the precession of the
It took Einstein 4 years (19001904) to find perihelion of Mercury. In his years at the
a suitable position, that of expert third-class, at Institute in Princeton, he and a few collaborators
the Patent Office in Bern, Switzerland. It has been elaborated the GRT, carrying it forward to the
plausibly argued that his duty of examining next stage of research. During those years,
applications submitted for electromagnetic Einstein also worked (in part with Peter
engineering devices helped him form critical Bergmann and Valentine Bargmann) on
ideas used in his special relativity, one of his a generalization of Theodore Kaluza's
several breakthrough publications in the golden higher-dimensional unification of electromagne-
year of 1905.
tism with relativity, which later served as an
Over time, Einstein's extraordinary talent introduction to contemporary investigations in
became acknowledged, and he accepted a series String Theory.
of academic appointments: at Zurich University Einstein responded to these (and later)
(1909), at the German University in Prague successes with inner self-confidence and outward
(1911), at his old Swiss Polytechnic Institute expressions of humorous self-derogation. He
(1912), and at the Friedrich-Wilhelm University once said his greatest gift was his stubbornness,
at Berlin (1914). Here, Einstein became well and his ability to remain intrigued by questions
established in the Prussian Academy of Sciences. that only children might ask. His personal behav-
It was his penultimate move in the long series, the ior and opinions often alarmed his more conven-
final relocation being to the Institute for tional colleagues, for he had "Bohemian"
Advanced Study in Princeton, New Jersey, in tendencies in demeanor and clothing, urged pac-
October 1933, where he remained to the end. ifism during World War I, and worked strenu-
His first visit to the United States took place in ously on behalf of arms control after World
1921, and he returned there for three working War II. Einstein expounded against nationalism
visits at the California Institute of Technology. and undemocratic, hierarchical rules; he made no
On returning to Europe from the last of these in secret of his being a Jew and in favor of zionism
early 1933, just when Hitler had been allowed to (if it accommodated the Arabs in Palestine).
come to power in Germany, Einstein refused to He opposed religious establishments in favor of
proceed to his home in Berlin. Indeed, he never a personal "cosmic religion," in the spirit of
set foot in Germany again.
Baruch Spinoza. In 1952, Einstein felt compelled
to decline the offer of the presidency of the State of Israel, feeling that he lacked the quality for leadership needed for the task. Some of these traits, when added to his exceptional scientific standing, conveyed on him a kind of charisma that still holds sway, although Einstein himself never understood it. It made him the target of attacks by anti-Semites and other enemies from 1920 onward (even threatening his life in 1922), but, on the other hand, flooded him with adoring or opportunistic appeals. A famous example of the latter occurred when three of his colleagues persuaded Einstein to sign the letter of 2 August 1939, warning President Franklin Delano Roosevelt of the danger that the Germans, then about to begin World War II, might construct atomic weapons (as they attempted to do before the Allies). What might have been the sources of Einstein's extraordinary imaginative powers? A reasonable though all-too-brief answer might begin by noting that each of his three main papers of 1905 on the quantized notion of light, on explaining Brownian motion, and on what Einstein called modestly a "modification of the teachings of space and time" (i.e., SRT) seems to be written on completely different topics. Yet, closer study shows that they all stemmed from one preoccupation, namely, with fluctuation phenomena; moreover, they have the same general style and components. Contrary to one of the popular images of how scientists work, Einstein did not start with some "crisis" brought about by puzzling new experimental facts (nor, contrary to opinions in textbooks, a seminal influence of the failure of the Michelson-Morley experiment). Rather, his dissatisfaction was focused on an asymmetry, or lack of generality in the then-current theory, that others might dismiss as merely aesthetic in nature. He proposed one or two principles, analogous to the axioms of Euclid, and then showed how consequences drawn from them would remove his dissatisfaction. At the end of each early paper, there was a brief and seemingly offhand proposal for experiments that might bear out the predictions of Einstein's theory.
For example, Einstein's paper on the quantum nature of light was motivated by noting an obvious point that the energy of a palpable body is concentrated and not infinitely divisible. But why should atomicity not apply to both matter and light energy? Here, one glimpses Einstein's fundamental, primary motivation in scientific work, announced in a 1901 letter to Marcel Grossmann: "It is a wonderful feeling to recognize the unity of a complex of appearances which, to direct sense experience, seem to be separate things." All of his 1905 papers endeavor to bring together and unify apparent opposites, removing the illusory barriers between them. Similarly, Einstein's GRT and attempted unified field theory arose from his dissatisfaction with his SRT, because the latter excluded gravitation and therefore seemed to him to require extension. As he once put it, he was driven by the "need to generalize." These observations intersect, finally, with Einstein's often-expressed interest in a guiding, practical philosophy of science. A key part of this approach was his recognition that a researcher initially cannot work "without any preconceived opinion." He referred to these preconceptions as "`categories' or schemes of thought, the selection of which is, in principle, entirely open to us, and whose qualification can only be judged by the degree to which its use contributes to making the totality of the content of consciousness `intelligible'." Einstein clearly interpreted such categories in a non-Kantian sense, i.e., as freely chosen. Like other major scientists, his loyalty to and use of presuppositions to which I refer as themata were powerful motivations and guides. Among the themata prominent in Einstein's theory constructions were the following: primacy of formal (rather than materialistic) explanation; unity (or unification, preferably on a cosmological scale); logical parsimony and necessity; symmetry; simplicity; completeness; continuity; constancy and invariance; and causality. In contrast, the quantum mechanics of Niels Bohr's school, with its concepts of fundamental probabilism and indeterminacy, rather than (classical) causality and
Elger, Thomas Gwyn Empy
completeness, was abhorrent to him, and largely associations in the late nineteenth and early twen-
explains the unresolved controversy between tieth centuries. An avid observer and popularizer,
Einstein and Bohr.
he is best known for his lunar map, considered
Of Einstein's thematic presuppositions, the one of the best available until the space age.
one that guided him most to success, but also to Elger lived most of his life in Bedford. His
his failure to achieve a unified field theory, was grandfather Isaac, his father Thomas Gwyn Elger
the concept of Einheit (unity), or, as he once (an architect and builder), and he all served as
put it, a longing to behold the preestablished Mayor of Bedford. After graduating from the
harmony that would lift one from the harshness Bedford Grammar School, he attended the
and dreariness of everyday life. Here one University College in London. Upon completion
glimpses why Einstein and his search, even if of his studies, he became a civil engineer and
uncomprehended in detail by laypersons, participated in the design of the Metropolitan
continues to be an icon for them.
Railway and the Severn Valley Railway.
When Elger inherited his father's estate in the
mid-1860s, he retired from civil engineering to
pursue scientific studies, including astronomy
and archaeology. Elger moved into his mother's
Einstein, Albert (1954). Ideas and Opinions. New York: Bonanza Books. (Reprint, New York: Modern Library, 1994.) FoЁlsing, Albrecht (1997). Albert Einstein: A Biography. New York: Viking.
home on Caldwell Street in Bedford and erected his first home observatory. Elger served on numerous Bedford city committees. He was a supporter of the Bedford Library and the Literary Institute,
Holton, Gerald (1988). Thematic Origins of Scientific Thought: Kepler to Einstein. Cambridge, Massachusetts: Harvard University Press. Holton, Gerald, and Yehuda Elkana (eds.) (1982). Albert Einstein, Historical and Cultural Perspectives: The
and a founder of the Bedfordshire Natural History Society and Field Club. Elger was elected a fellow of the Royal Astronomical Society on 10 February 1871. His
Centennial Symposium in Jerusalem. Princeton: Princeton University Press. Pais, Abraham (1982). "Subtle Is the Lord . . .": The Science and the Life of Albert Einstein. Oxford: Oxford University Press.
astronomical observing program was at first a broad one, as evidenced by his early papers, published in Monthly Notices of the Royal Astronomical Society. Observations of the colors of the
Schilpp, Paul Arthur (ed.) (1949). Albert Einstein: Philosopher-Scientist. Evanston, Illinois: Library of Living Philosophers. Stachel, John (ed.) (1987). The Collected Papers of Albert Einstein. Princeton: Princeton University Press.
double-star g Delphini (1872), observations of Venus (1873), observations of Saturn (1887), and important work on Saturn's Crepe ring (1888). However, Elger's major astronomical
preoccupation was the Moon, which he observed
and wrote about extensively. As he became
recognized as an authority on the Moon, Elger
Elger, Thomas Gwyn Empy
wrote the chapters on the Moon for various
editions of Thomas Webb's book Celestial
Robert A. Garfinkle
Objects for Common Telescopes and for
Union City, CA, USA
Astronomy for Amateurs, a Practical Manual of
Telescopic Research in All Latitudes Adapted to
the Powers of Moderate Instruments (1888),
Born Bedford, England, 27 October 1836
edited by John A. Westwood Oliver.
Died Bedford, England, 9 January 1897
In 1895, Elger published his classic work The
Moon : A full Description and Map of its
Thomas Elger, one of the preeminent amateur Principal Physical Features. This popular book
lunar observers of the Victorian era, was contained his lunar map, in four sections on
a leader in British amateur astronomical a scale of 18 in. to the Moon's diameter, and his
Elkin, William Lewis
descriptions of all of the named features on the nearside. Elger also had the map published as a separate sheet. Elger's map was regarded as one of the better lunar maps until the space age. The map was updated by English selenographer Hugh Wilkins and republished in 1959. From 1887 until near his death, Elger contributed a monthly column "Selenographical Notes" to The Observatory. His lunar observations also appeared in a long series of articles in the English Mechanic. Elger published the article "Lunar Work for Amateurs" in the Publications of the Astronomical Society of the Pacific in June 1891. In that paper he explained how a novice observer could get started observing the Moon. Elger showed the same zeal for participation in astronomical organizations that was reflected in his civic life. From the founding of the Selenographical Society in 1878 until its folding in 1882, Elger was a member and a regular contributor of lunar observations to the Selenographical Journal. Elger was an early and active member of The Liverpool Astronomical Society [LAS], founded in 1881, serving as LAS president for 1 year (1888/1889) and as director of its lunar section for several years. In 1890, after the collapse of the LAS, Elger was a founding member of the British Astronomical Association and served as the first director of the association's Lunar Section. He edited the first three "Reports of the BAA Lunar Section" (1891, 1893, and 1895). Elger suffered a stroke on 29 December 1896, and died from heart failure as well as the effects of the stroke. He was survived by his widow, Fanny Edith, whom he had married in 1880, and by his two young sons. Shortly after his death, the last of his nearly 200 "Selenographical Notes" in The Observatory magazine was published. A nearside lunar crater at latitude 35 30 S, longitude 29 80 W was named in Elger's honor in 1912. Selected References Anon. (18961897). "Thomas Gwyn Empey Elger." Journal of the British Astronomical Association 7, no. 4: 207208.
Anon. (1897). "Thomas Gwyn Empy Elger." Monthly Notices of the Royal Astronomical Society 57: 210211. (This obituary gives his birth year as 1837, but all other sources list 1838.) Elger, Thomas Gwyn (1895). The Moon: A Full Description and Map of Its Principal Physical Features. London: George Phillip and Son. Sheehan, William P. and Thomas A. Dobbins (2001). Epic Moon: A History of Lunar Exploration in the Age of the Telescope. Richmond, Virginia: Willmann-Bell. Whitaker, Ewen A. (1999). Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature. Cambridge: Cambridge University Press. Elkin, William Lewis Thomas R. Williams Rice University, Houston, TX
, USA Born New Orleans, Louisiana, USA, 29 April 1855 Died New Haven, Connecticut, USA, 29 May 1933 Using the Yale heliometer, William Elkin measured the parallax of over 200 stars, an unprecedented productivity with that instrument. Working with David Gill, Elkin contributed to the accurate measurement of the solar parallax by measuring the parallax of asteroids, and was among the first to apply photography to meteor astronomy. Elkin was the son of Lewis Elkin, a teacher, private-school owner, and successful carpet manufacturer in New Orleans. His mother Jane (neґe Fitch), a native of Thetford, Vermont, met and married Lewis after moving to New Orleans. William was the only survivor of the five siblings born to their marriage. In 1867, Lewis was appointed commissioner to represent the state of Louisiana at the Paris Exhibition, but within days of the family's planned departure, he died. Friends who were to travel to Paris with the family prevailed on Jane Elkin to make the trip in spite of her tragedy; the family remained in Europe for 17 years. While living in Switzerland in 1870, William Elkin fell ill, probably with
Elkin, William Lewis
a severe case of dysentery, and remained physi- stars, and to confirm with certainty that they
cally frail for the rest of his life. The family lived moved in a common direction as members of the
in a number of countries with the result that cluster.
Elkin's early education was broad; he acquired Elkin also measured all of the stars he could excellent skills in French and German and pass- see within 1000 of the North Celestial Pole,
ing ability in Italian and Spanish. He achieved Harvard's North Polar Sequence, at the request
a baccalaureate degree in civil engineering from of Edward Pickering. He next undertook to
the Royal Polytechnic School in Stuttgart, determine the parallax of the ten northern
Germany, but during that experience came to first-magnitude stars and tied those into the results
prefer astronomy as a lifetime occupation.
that he and Gill had first reported. While his accu-
Elkin studied astronomy with Friedrich rate parallax determinations are important individ-
Winnecke, director of the Strasbourg Observa- ually, a more important conclusion that Elkin drew
tory, where his fellow graduate students included from the work that he and Gill had completed was
Karl Kustner and Carl Hartwig. During that for the most part, the brightest stars are not
his last year in graduate school, Elkin spent necessarily close to the Earth, but instead are
30 min in conversation with Gill, who had only intrinsically very bright. On the other hand, stars
recently been appointed Her Majesty's Astrono- with large proper motions were clearly much
mer at the Cape of Good Hope and was passing closer to the Earth and therefore better candidates
through Strasbourg. They agreed on the impor- for accurate heliometric measurements.
tance of the heliometer as an instrument of posi- Elkin, with two assistants, Frederick L. Chase
tional astronomy and Gill, taken with his younger and Mason Smith, undertook a program to mea-
colleague's knowledge and personality, invited sure the parallax of all stars with large proper
Elkin to come to the Cape for a visit of several motions. The result of this program was the addi-
years' duration. Their friendship, formed tion of another 238 parallaxes to the catalog, an
securely in that brief discussion, lasted until accomplishment that Frank Schlesinger rated
Gill's death some 35 years later. After defending as the most important contribution to the knowl-
a dissertation on the parallax of a Centauri, Elkin edge of stellar distances up to that time. It was for
was awarded a Ph.D in 1880. He accepted Gill's this work that the French Academy of Sciences
invitation and was in residence at the Cape of awarded Elkin the Lalande Prize in 1908.
Good Hope as part of the Gill family from early Elkin next took on a cooperative program with
1881 until 1884.
Gill to determine the solar parallax using aster-
At the Cape Observatory, Elkin worked for oids. Between 1888 and 1894 he observed minor
several years with Gill, doing heliometric paral- planets (7) Iris, (12) Victoria, and (80) Sappho in
laxes. Working together on two separate heliome- this program, but was unable to participate in the
ters, they established, with considerable accuracy, Eros campaign because of the faintness of the
the parallax of nine first-magnitude Southern asteroid and its unfavorable location for heliom-
Hemisphere stars. On the basis of the reputation eter measurements from New Haven. Observato-
thereby established, Elkin was employed by Yale ries at Oxford, England, and Leipzig, Germany,
University in 1884 and moved to New Haven, participated, along with Yale Observatory and
Connecticut, with his mother. He was the first the Cape Observatory. The solar parallax derived observer who would make routine measurements from these measures, 8.80200 with a probable with the Yale heliometer. Elkin's first program at error of only 0.00500, was more confidently
Yale University was to reobserve the Pleiades for accepted than measures derived from the transits
comparison with Friedrich Bessel's observa- of Venus. Equally important consequences of
tions (then 50 years old). Of the 69 stars for this work were the subsidiary determinations of
which Elkin established accurate relative places, the mass of the Moon, constants of nutation
he could compare his results with those of Bessel and aberration, the dynamic flattening of the
well enough to derive proper motions for 51 of the Earth, and refinement of the lunar equation.
From 1891 to 1892 Elkin was also involved in a program to determine the orbits of Jupiter's satellites and, from those data, he recomputed the mass of Jupiter. Elkin was the first astronomer in America to use photography for meteor observation. His Geminid radiant in 1893 was based on only three meteors, but they intersected in an incredibly small area that left little doubt. Elkin further attempted to determine meteor velocities using a rotating sector disk to mark the photographic tracks into precise segments. While many altitudes were determined with simultaneous photographs taken from two stations in this program, Elkin was never satisfied with the probable errors and problems associated with his observations. In addition to the Lalande Prize mentioned above, Elkin was honored by election as a Foreign Associate of the Royal Astronomical Society, and by election to the National Academy of Sciences. In June 1896, Elkin replaced Hubert Newton as the director of the Yale Observatory, a position he held until his retirement in 1910. Elkin had married Catherine Adams of New Haven in 1896; their marriage remained childless, but they enjoyed common interests in music and photography during his lengthy retirement. Selected References Hoffleit, Dorrit (1992). "Astronomy at Yale, 17011968." In Memoirs of the Connecticut Academy of Arts and Sciences. Vol. 23, pp. ixvii and 1230. New Haven: Connecticut Academy of Arts and Sciences. Schlesinger, Frank (1938). "Biographical Memoir of William Lewis Elkin." Biographical Memoirs, National Academy of Sciences 18: 175188. Ellerman, Ferdinand Peter Riley University of Texas, Austin, TX, USA Born Centralia, Illinois, USA, 13 May 1869 Died Pasadena, California, USA, 20 March 1940
Ellerman, Ferdinand. Courtesy of The Observatories of the Carnegie Institution of Washington A skilled and dedicated solar and stellar spectroscopist and photographer, Ferdinand Ellerman's professional relationship with George Hale lasted 46 years, and involved him in the design and construction as well as the operation of two major observatories. Ellerman can rightly be credited with conducting the majority of the observational projects through which Hale's early discoveries were achieved. Ellerman was educated in local Illinois schools and moved to Chicago in 1886, where he worked in several commercial organizations, developing exceptional abilities in photography and in the use of machine tools. This unusual combination of skills attracted the attention of young Hale, who in 1892 hired Ellerman as an assistant at his private observatory, in Kenwood, Illinois. Ellerman followed Hale to Yerkes Observatory in 1895, and to Mount Wilson Solar Observatory in 1905. He was a member of the Astronomical Society of the Pacific and of the American Astronomical Society, and in 1912 received an honorary Masters degree from Occidental College. Ellerman retired from Mount Wilson Solar Observatory in 1938.
Ellery, Robert Lewis John
Ellerman's work was carried out in close
collaboration with Hale, who always duly Ellery, Robert Lewis John
acknowledged the importance of Ellerman's con-
tributions. Ellerman was heavily involved in the Julian Holland
development and use of the spectroheliograph. He University of Sydney, Darlington, NSW,
carried out a good share of the solar observational Australia
work at Yerkes Observatory and Mount Wilson
Solar Observatory, leading to the discovery of new
solar phenomena, such as solar vortices and vari- Born Cranleigh, Surrey, England, 14 July 1827
ous properties of the magnetic fields of the Sun and Died Melbourne, Victoria, Australia,
of sunspots. He also obtained most of the night- 14 January 1908
time observations for Hale's research program on
carbon stars. Ellerman's instrumental skills played Robert Ellery was director of the earliest perma-
an important role in the development of Mount nent observatory in Australia and directed the
Wilson Solar Observatory, which he had already installation and initial operation of the Great
visited in 1904 with Hale. Ellerman took on the Melbourne Telescope, the first large reflecting
responsibility for the solar photographic program telescope in the Southern Hemisphere. The son
at Mount Wilson Solar Observatory, and the "tem- of John Ellery, a surgeon, and his wife Caroline
porary" focal-plane solar camera he constructed in (neґe Potter), Robert Ellery attended the local
1905 for the Snow telescope proved so superior to grammar school and was trained for a medical
its attempted successor that it was never replaced, career. However, his growing interest in astron-
and remains in use to this day.
omy led to contact with Greenwich Observatory
Throughout his life, Ellerman remained where he developed friendships with the staff and
involved in civic affairs, serving on school boards became acquainted with the use of instruments,
in Williams Bay, Wisconsin (home community to eventually becoming a professional astronomer.
Yerkes Observatory) and Pasadena, California. In 1851 Ellery immigrated to the Australian
A lover of the outdoors, Ellerman was fondly colony of Victoria. The increase in shipping asso-
remembered by many visitors to Mount Wilson ciated with the gold rush created the need for
Solar Observatory for his guided hiking, climbing, accurate time for rating chronometers. Ellery pro-
and fishing excursions in the neighboring hills. posed to the Melbourne press that a nautical
observatory be established at nearby
Williamstown. The government responded by
appointing Ellery to run the modest establishment in 1853.
Adams, Walter S. (1940). "Ferdinand Ellerman." Publi-
Almost single-handedly Ellery built up
cations of the Astronomical Society of the Pacific 52: a functioning observatory. The first telegraph
165168. (This obituary notice written by Ellerman's colleague remains a primary source of biographical information.) Ellerman, Ferdinand (1917). "Solar Hydrogen `Bombs.'" Astrophysical Journal 46: 298300.
line in the colony connected Williamstown to Melbourne to coordinate the simultaneous dropping of time balls. By then, Ellery's standing was such that, in addition to his astronomical
Hale, George E. and Ferdinand Ellerman (1899). "On the Spectra of Stars of Secchi's Fourth Type. I." Astrophysical Journal 10: 87112. -- (1904). "Calcium and Hydrogen Flocculi." Astrophysical Journal 19: 4152.
duties, he was appointed director of the geodetic survey begun in 1856. A new observatory, superseding both the Williamstown operation and Dr. Georg
-- (1906). "The Five-foot Spectroheliograph of the Solar Observatory." Astrophysical Journal 23: 5463. Hale, George E., Ferdinand Ellerman, S. B. Nicholson, and A. H. Joy (1919). "The Magnetic Polarity of SunSpots." Astrophysical Journal 49: 153178.
Neumeyer's Meteorological and Magnetic Observatory, was established in Melbourne in 1863 with Ellery as director. This new observatory provided the focus for reviving a plan for
Ellery, Robert Lewis John
a large reflecting telescope in the Southern Hemisphere. Sir Edward Sabine, and later, in 1849, Thomas Robinson of Armagh Observatory, proposed such a telescope to continue John Herschel's observations of nebulae at the Cape of Good Hope, but the idea was abandoned when George Airy failed to support it. With interest expressed from Melbourne in 1862, the scheme was revived and a giant reflector ordered from Thomas Grubb of Dublin in 1866. This Cassegrain telescope with equatorial mounting and a 48-in. speculum metal primary mirror was installed in 1869. The intended use of the telescope was primarily to document southern nebulae by hand drawing. Excessive vibration of the telescope tube under the influence of local winds and other factors combined to make visual observation with the telescope difficult. Despite difficulties with the new telescope, Ellery's assistants made some fine drawings of nebulae. Unfortunately, although the hand-drawn representations of nebulae were well done, they could not reasonably be compared with earlier observations made with smaller telescopes and under different conditions. Excellent photographs of the Moon were taken in the 1870s and for a period were considered the best available. The Great Melbourne Telescope was among the last in the tradition of large reflectors constructed in Ireland in the nineteenth century, and in some respects perhaps the finest. Nevertheless, it was at best a mixed blessing. It was not possible to publish the delicate nebula drawings. The telescope was not sufficiently stable to allow for the long exposures necessary for either nebular or stellar photography, nor was it suited for spectroscopy. Ellery's skill in refiguring and polishing one of the 48-in. mirrors of the Great Melbourne Telescope made it "undoubtedly more perfect in figure than it ever has been" (Annual Report for 1890, p. 6). Despite this, the achievements of the observatory largely depended on other instruments. A 5-in. transit circle delivered by Troughton & Simms in 1861 was used for meridian observations until 1884 when the same firm delivered an 8-in. instrument modeled on the transit circle
at Cambridge Observatory. Ellery's mastery of meridian astronomy is reflected in the series of general catalogs of meridian observations of stars published in 1869, 1874, and 1889. Airy commented, in the mid 1870s, that the Melbourne catalogs of Southern Hemispheric stellar positions were the best that had been published. The last major undertaking during Ellery's directorship was Melbourne Observatory's share in the Carte du Ciel, the international astrographic mapping project initiated in Paris in 1887. Australian participation in the project was agreed to by Henry C. Russell, director of Sydney Observatory, with the declination zone А65 to the South Celestial Pole assigned to Melbourne Observatory. The venture began with great enthusiasm, and exposures of the plates at both observatories were completed in a timely manner. Measurement of the plates for both Sydney Observatory and Melbourne Observatory was carried out at the latter observatory until 1915. The plates were eventually transferred to Sydney where the measurements were finally completed. Victoria suffered severely in the financial depression of the early 1890s, leading to cutbacks of staff at the observatory. Ellery retired in 1895 but continued to live at Observatory House and was appointed to the observatory board of visitors. Ellery was associated with many official and public bodies
in Victoria in addition to his work at the observatory. He headed the Geodetic Survey until 1874, served with the Torpedo Corps of the local Volunteer Force, and presided at the Intercolonial Meteorological Conferences held in Melbourne in 1881 and 1888 and at the meeting of the Australasian Association for the Advancement of Science there in 1900. Ellery joined the Royal Society of Victoria in 1856, serving as its president from 1866 to 1885, and published numerous papers in its journal. He was also a keen apiarist. His achievements and services were recognized by his election as a fellow of the Royal Astronomical Society (1859) and fellow of the Royal Society (1863). In 1889, he was awarded the Companion of Saint Michael and Saint George [CMG].
In 1854 Ellery married Jane Shields, but she Ellicott was the son of clockmaker Joseph
died 4 years later. He married Jane's younger Ellicott and his wife Judith Bleaker. His early
sister, Margaret, in 1859. Enfeebled by an attack education was completed at a Quaker school in
of paralysis, Ellery died at Observatory House, Solesbury, Pennsylvania. At the age of 15, he
survived by his second wife and a daughter from began to study physics, mathematics, and astron-
his first marriage.
omy under Robert Patterson (who later taught
those subjects at the University of Pennsylvania).
Ellicott's family moved to Baltimore County,
Maryland, in 1772 and likewise operated
a milling business. In 1775, he married Sarah Anon. (1860-). Annual Reports of the Government Astron- Brown; the couple had ten children. During the
omer. Melbourne. Anon. (15 January 1908). "Obituary". Argus (Melbourne).
Revolutionary War, Ellicott served with the
Anon. (1908). "Obituary". Proceedings of the Royal Soci- Maryland militia and rose to the rank of captain
ety of Victoria 21: 553.
(later major). After his father's unexpected death
Gascoigne, S. C. B. (1992). "Robert L. J. Ellery, His Life and Times." Proceedings of the Astronomical Society of Australia 10, no. 2: 170176. --. (1995). "The Great Melbourne Telescope and Other 19th Century Reflectors." Historical Records of Aus-
in 1780, he managed both the mills and the family's clockmaking enterprise. Ellicott's skills as a surveyor were called upon when he was appointed to a commission
tralian Science 10, no. 3: 233245. Glass, Ian S. (1997), Victorian Telescope Makers: The Lives of Thomas and Howard Grubb. Bristol: Institute of Physics, pp. 3961. H. H. T. (1909). "R. L. J. Ellery, 18271908." Proceed-
(1784) that surveyed the boundary between Pennsylvania and Virginia (now West Virginia), a process requiring 6 months of hard labor. He also participated (with Philadelphia astronomer
ings of the Royal Society of London A 82: vix King, Henry C. (1979). The History of the Telescope. New York: Dover, esp. pp. 264267. Perdrix, John L. (1992). "The Last Great Speculum: The 48-inch Great Melbourne Telescope." Australian
David Rittenhouse) in the survey that established the western boundary of Pennsylvania (1786), and in 1787 he surveyed the state's northern boundary (on the 42nd parallel of lati-
Journal of Astronomy 4: 149163.
tude), which later included the Presque Isle trian-
gle (now Erie, Pennsylvania). For making
latitude observations, Ellicott preferred to use
a zenith sector, while many of his longitude
measurements were derived from observations
of the eclipses of Jupiter's Galilean satellites,
Jordan D. Marcheґ II
especially Io. During a visit to Philadelphia,
University of Wisconsin, Madison, WI, USA Ellicott was elected to the American Philosophi-
cal Society; in 1789, he relocated his family to
Born Buckingham, Pennsylvania, (USA),
In 1791, Ellicott was appointed by President
24 January 1754
George Washington to survey the 10-mile-square
Died West Point, New York, USA,
tract of land ceded from Maryland and Virginia
20 August 1820
that became the District of Columbia, future
site of the nation's capital. At first working
American mathematician, surveyor, and astrono- under difficult wintertime conditions, he was
mer, Andrew Ellicott laid out the nation's capital, assisted for several months by the African Amer-
trained Meriwether Lewis to conduct astronomi- ican almanac-maker Benjamin Banneker.
cal observations on the Corps of Discovery's Ellicott's survey was not completed until 1793;
expedition with William Clark, and became his account of the astronomical observations
a professor of mathematics in the United States was later published in the Transactions of the
Military Academy at West Point, New York.American Philosophical Society
Ellison, Mervyn Archdall
With his reputation established, Ellicott was again appointed by Washington in 1796 to work with Spanish commissioners to establish the boundary between the United States and the Spanish territory of Florida, along the 31st parallel of latitude. This enormous undertaking stretched from the Atlantic Ocean to the Mississippi River and occupied Ellicott and his assistants from 1798 to 1800. While off the territory's coast in November 1799, Ellicott observed the great Leonid meteor storm and reported: About two o'clock in the morning I was called up to see the shooting of the stars (as it is vulgarly termed), the phenomenon was grand and awful, the whole heavens appearing as if illuminated with sky rockets, flying in an infinity of directions, and I was in constant expectation of some of them falling on the vessel. They continued until put out by light of the sun after daybreak. In the conduct of his survey, Ellicott also made numerous observations on the region's flora and fauna, which in turn were described in his publication of the results (The Journal of Andrew Ellicott. . . (1803)). As a reward for these labors, he was offered (but declined to accept) the post of surveyor-general of the United States, extended by President Thomas Jefferson
. Ellicott urged Jefferson to support the establishment of a national observatory. In 1801, Ellicott was appointed by the governor of Pennsylvania as secretary of the State's Land Office and thus relocated to Lancaster, Pennsylvania, whose latitude and longitude he promptly determined. He maintained a correspondence with Jefferson and French astronomer Jean Delambre. At Jefferson's request, Ellicott trained Meriwether Lewis (between April and May 1803) in the use of a sextant, chronometer, and other astronomical instruments to be used on Lewis and Clark's exploration and mapping of the Louisiana territory. Following a political turnover in 1808, Ellicott was dismissed from the Land Office but was chosen in 1811 to survey the northern boundary between Georgia and North Carolina. In 1813, he was appointed professor of mathematics at West Point by President James Madison and retained this position until his death.
The Georgian-style building from which Ellicott operated the Pennsylvania Land Office, at 123 North Prince Street, Lancaster, was completely restored in 1981 (as the SehnerEllicott-von Hess House). It is listed on the NATIONAL REGISTER OF HISTORIC PLACES
and is now occupied by the Historic Preservation Trust of Lancaster County. Three of Ellicott's telescopes are preserved at the National Museum of American History, Smithsonian Institution
, while his papers can be found in the Library of Congress and the United States National Archives
. Selected References Ambrose, Stephen E. (1996). Undaunted Courage: Meriwether Lewis, Thomas Jefferson, and the Opening of the American West. New York: Simon and Schuster
, esp. pp. 8688. Bedini, Silvio A. (1999). "Ellicott, Andrew." In American National Biography, edited by John A. Garraty and Mark C. Carnes. Vol. 7, pp. 415416. New York: Oxford University Press. Ellicott, Andrew (1962). The Journal of Andrew Ellicott, late commissioner on behalf of the United States . . . for determining the boundary between the United States and the possessions of his Catholic Majesty . . . . Chicago: Quadrangle Books
. (Originally published 1803.) -- (1964). Plan of the city of Washington in the territory of Columbia: ceded by the States of Virginia and Maryland to the United States of America, and by them established as the seat of their government, after the year MDCCC. Ithaca, New York: Historic Urban Plans. (Originally published 1792.) Greene, John C. (1984). American Science in the Age of Jefferson. Ames: Iowa State University Press, esp. pp. 134144. Mathews, Catherine van Cortlandt (1908). Andrew Ellicott: His Life and Letters. New York: Grafton Press. Ellison, Mervyn Archdall Ian Elliott Dunsink Observatory, Dublin, Ireland Born Fethard-on-Sea, County Wexford, Ireland, 5 May 1909 Died Dublin, Ireland, 12 September 1963
Ellison, Mervyn Archdall
Ellison entered Trinity College, Dublin, in
1927 to read physics under Professor
R. W. Ditchburn. He had a brilliant academic
career, graduating with a first class honors degree
in experimental physics and gaining an M.
Sc. degree in 1932. Before his mother's death in
1933, Ellison spent a year teaching at Armagh
Royal School before his appointment as senior
science master at Sherborne School, Dorset. In
1934 he married Patricia, only daughter of
Crosthwaite Herron, MD of Armagh. They had
one son and two daughters.
At Sherborne, Ellison constructed his own
spectrohelioscope after the design of George
Hale, grinding and polishing his own mirrors and
lenses. He used this instrument to observe solar
flares in hydrogen-alpha (Ha) light; the results
were published in the Monthly Notices of the
Royal Astronomical Society. During World War
II, Ellison served in the Operational Research
Group of the Admiralty under professor
Patrick Blackett. When Ellison returned to Ellison, Mervyn Archdall. Reproduced by permission of Sherborne, a very high sunspot maximum was Mr. J. C. Liddell in progress. He fitted a spectrograph to his spec-
Mervyn Ellison was a solar astronomer of inter- troheliograph so that after locating an interesting
national repute. As an amateur and later as chromospheric feature, he could take its spec-
a professional, Ellison studied solar flares and trum. On 25 July 1946 Ellison obtained a superb
their terrestrial effects.
spectrum of a great flare over a giant sunspot that
Ellison was the third son of the distinguished showed the Ha line in emission extending for amateur astronomer and telescope maker, 20 A° . He continued visual monitoring of flares
Reverend William Frederick Archdall Ellison and showed that for intense flares the peak inten-
(18641936), rector of Fethard-on-Sea with sity had a short duration, which he termed the
Tintern in County Wexford from 1908 until "flash phase."
1918 when he was appointed director of Armagh Ellison began his professional career in 1947
Observatory. In 1920 the elder Ellison published with his appointment as principal scientific offi-
The Amateur's Telescope, which was the forerun- cer and deputy director at the Royal Observatory,
ner of the famous three-volume set on amateur Edinburgh. The Sherborne instrument was
telescope making edited by Albert Ingalls. remounted at Edinburgh so Ellison could con-
Mervyn Ellison was educated at home and later tinue his studies of flares and prominences. He
at Armagh Royal School. He acquired his practical adopted photometric methods for measurement
skills in astronomy from his father and had full of flare brightness in order to follow the
access to the telescopes of Armagh Observatory. change of flare intensity with time. Ellison used
At the age of 13, he was making detailed drawings long-wave radio receivers to record disturbances
of sunspots and features on Mars and Jupiter. of the ionosphere and to correlate these with
Ellison's micrometric observations of double solar activity. The results of his work over
stars with the 10-in. Grubb refractor resulted in 11 years in Edinburgh were published in the
his first paper being accepted for publication by Publications of the Royal Observatory,
the Royal Astronomical Society.
Edinburgh and in the Monthly Notices of the
Elvey, Christian Thomas
Royal Astronomical Society. During this time Ellison was a joint editor for The Observatory for 5 years. His popular book The Sun and Its Influence was published in 1955 and later translated into Russian and Spanish. In 1952 the United Kingdom National Committee for the International Geophysical Year [IGY] invited Ellison to be its representative for solar activity. From 1955 he became a member of the committee for the study of solar-terrestrial relationships under the International Council of Scientific Unions. Later he was appointed world reporter for solar activity of the IGY, which began in July 1958. Early in 1958 Ellison went to South Africa to install an automatic Lyot heliograph at the Royal Observatory, Cape of Good Hope, as part of Britain's contribution to the IGY. The heliograph took 35-mm photographs of the full disk of the Sun in Ha light at 1-min intervals. In November 1958 Ellison was appointed senior professor in the School of Cosmic Physics of the Dublin Institute for Advanced Studies; he took up residence at Dunsink Observatory. The Cape and Dunsink observatories operated the heliograph jointly for the next 5 years. The results were published in Dunsink Observatory Publications, Vol. 1, nos. 14 under the joint authorship of Ellison, Susan M.P. McKenna, and John H. Reid. With the conclusion of the IGY, as general editor Ellison had the onerous task of organizing the publication of daily charts showing every solar feature. This great work appeared as Vols. 21 and 22 of the Annals of the International Geophysical Year. In 1963 Ellison was making plans for the International Quiet Sun Year. He was to have chaired a committee meeting at Berkeley, California, USA, in June. However, he had to cancel his attendance on account of an illness that soon proved fatal. In a tribute, Ellison's lifelong friend, Eric Lindsay of Armagh Observatory, praised "his characteristic simplicity, unbiased judgment, wise administration, and loyal friendship." Ellison was elected a fellow of the Royal Astronomical Society in 1938 and served on its
council from 1940 to 1950. He was elected a fellow of the Royal Society of Edinburgh in 1944 and was awarded the D.Sc. of the University of Dublin in 1944. Ellison was Vice-president of Commission 10 of the International Astronomical Union, a member of the Royal Irish Academy, and a member of the British Astronomical Association. The International Astronomical Union named the lunar crater at 55 10 N and 107 50 W in his honor. Selected References Bennett, J. A. "Ellison: the Director as Amateur." In Church, State and Astronomy in Ireland: 200 Years of Armagh Observatory, pp. 171178. Armagh: Armagh Observatory in association with the Institute of Irish Studies and the Queens' University of Belfast. Ellison, M. A. (1955). The Sun and Its Influence. London: Routledge and Kegan Paul
. (2nd ed. 1959; Russian edition: Moscow State Publishing House, 1958; Spanish edition: Mexico University Press, 1958.) Ellison, M. A., Susan M. P. McKenna, and J. H. Reid (19601963). "Cape Lyot Heliograph Results." Dunsink Observatory Publications 1, nos. 14. -- (ed.) (1962). IGY Solar Activity Maps. Annals of the International Geophysical Year, Vols. 21 and 22. Oxford: Pergamon Press. Ellison, W. F. A. (1920). The Amateur's Telescope. Belfast: R. Carswell and Son. (This was the forerunner of the famous three-volume Amateur Telescope Making, edited by A. G. Ingalls. New York: Scientific American, 1935 and subsequent editions.) Newton, H. W. (1964). "Mervyn Archdall Ellison." Quarterly Journal of the Royal Astronomical Society 5: 5659. Wayman, Patrick A. (1987). "The Years 19581963: Mervyn Archdall Ellison." In Dunsink Observatory, 17851985: A Bicentennial History, pp. 229241. Dublin: Dublin Institute for Advanced Studies and Royal Dublin Society. Elvey, Christian Thomas Gary A. Wegner Department of Physics & Astronomy, Dartmouth College, Hanover, NH, USA Born Phoenix, Arizona, USA, 1 April 1899 Died Tucson, Arizona, USA, 25 March 1970
American stellar astronomer and geophysicist stellar atmospheres and stellar rotation. Elvey
Christian Elvey contributed to the discovery of was also interested in galactic nebulae and,
stellar rotation and the mapping of the interstellar while at McDonald Observatory, conducted stud-
medium. He was the son of John A. and Lizzie ies of nebular spectra with a special 150-ft nebu-
Christina (Neґe Miller) Elvey and married lar spectrograph. A 1930 paper with Albrecht
Marjorie Purdy in 1934. They had two children, UnsoЁld and O. Struve determined the density and
Thomas Christian and Christena Vivian. Elvey distribution of the interstellar medium using the
earned an AB (1921) and AM (1923) at the Uni- strengths of the interstellar Ca II lines for the first
versity of Kansas and was instructor in astronomy time. In 1932 Elvey began to publish papers on
there (19211925). Following fellowships in light from the gegenschein and the day and
astronomy at the University of Chicago the night sky. From about 1948 Elvey published
(19251926), he did research at the Dearborn papers on the night sky and aurorae and pioneered
Observatory and was instructor in astrophysics in making observations from aircraft.
at Northwestern University (19261928). From The University of Alaska awarded Elvey an
1928 Elvey worked at the Yerkes Observatory, honorary doctorate in 1969 at the opening of
notably with Otto Struve, earning a Ph.D. from the C. T. Elvey building named in his honor.
the University of Chicago (1930) with a thesis on A 74-km-diameter lunar crater is named for him.
the contours of spectral lines in the spectra of
stars. His thesis demonstrated that many stars Selected References have detectable rotation and that the rotation
periods for close binary systems are often syn- Anon. (1968). "Elvey, Christian Thomas." In Who Was
chronized with their orbital periods. Elvey
Who in America, Vol. 5, p. 214. Chicago: Marquis
remained as assistant professor at the University of Chicago until 1935, when he became astronomer and assistant to the director of McDonald Observatory. In Texas, he developed an interest
Who's Who. Elvey, C. T. (1930). "A Study of the Relations between the Observed Contours of Spectral Lines and the Physical Properties of the Stars." Ph.D. diss., University of Chicago.
in the diffuse light of the night sky. From 1942 to 1951 he studied the sky and the aurorae from the Naval Ordnance Test Station at Inyokern, California, progressing to head of staff. In 1952,
--. (1930). "The Contours of Hydrogen Lines in Stellar Spectra." Astrophysical Journal 71: 191208. --. (1930). "The Rotation of Stars and the Contours of Mg + 4481." Astrophysical Journal 71: 221230. UnsoЁld, A., O. Struve, and C. T. Elvey (1930). "Zur
Elvey moved to the University of Alaska in Fairbanks where he was head of the department of
Deutung der interstellaren Calciumlinien." Zeitscrift fur Astrophysik 1: 314325.
geophysics and director of the Geophysical Insti-
tute (19521963), vice president for Research
and Advanced Science (19611963), and Univer- Emden, Robert
sity Research Professor (19631967). He was
president of the Geomagnetism and Astronomy Ian T. Durham
Section of the American Geophysical Union Saint Anselm College, Manchester, NH, USA
[AGU] (19611964) and member of several
other scientific societies.
Elvey was interested in stellar spectra and Born Saint Gallen, Switzerland, 4 March 1862
studied a wide range of subjects from the 1920s Died Zurich, Switzerland, 8 October 1940
to the 1940s. With Struve and others at Yerkes
and McDonald observatories, he determined Swiss-German theoretical physicist Robert
spectroscopic binary orbits and made studies of Emden is best known for the Lane-Emden
line strengths and the profiles of hydrogen and equation, which can be used to describe the inter-
helium lines in stellar spectra. His work in spec- nal structure of gaseous spheres (stars) under
troscopy strongly contributed to understanding certain simplifying assumptions.
Empedocles of Acragas
Emden was educated in Switzerland and Germany and married the sister of Karl Schwarzschild. He was appointed professor of physics at the Technische Hochschule in Munich in 1889 and as professor of meteorology there in 1907. He was named honorary professor of astrophysics at the University of Munich in 1924, retiring in 1934 and returning to Switzerland. A primary goal of studies of stellar structure in that period was to be able to describe the internal distribution of temperature, pressure, and density in terms of physics known from terrestrial laboratories and use this description to try to understand the observed relationships among stellar masses, sizes, brightnesses, and surface temperatures. The pioneering investigation was that of Jonathan Lane who, in 1870, wrote "On the theoretical temperature of the sun, under the hypothesis of a gaseous mass maintaining its volume by internal heat and depending on the laws of gases as known to terrestrial experiments." This was followed and amplified by the investigations by August Ritter and William Thomson (Lord Kelvin). The latter was particularly certain that the source of solar and stellar energy was gravitational contraction, and the energy release therefore distributed throughout the volume. These investigations culminated in the work of Emden in the early twentieth century. His equations described stars as polytropes, i.e., gases with particularly simple relationships between pressure and density, measured by a single index, n, whose numerical value could be anything between 0 and 5. The key feature of these solutions, called polytropes, is that they do not require you to know what the energy source is, but only to know that pressure must balance gravity for stars to be stable and that energy must be transported outward fast enough to maintain observed luminosities. (Emden's work on the structure of the Sun and stars occurred during the period when the only known energy source was gravitational contraction, so his 1907 estimate of the age of the Sun was 22 million years.) Emden himself calculated tables of numerical solutions to the equations for a number of values
of n, which continued to be used well down into the era of early digital computers. Somewhat later, Arthur Eddington showed that n ј 3 corresponds to a star made of an ideal gas. Then Ralph Fowler found that n ј 3/2 describes a completely degenerate star or white dwarf. William B. Bonnor in 1956 applied these ideas to homogeneous, isotropic models of the Universe. The solutions are called Bonner-Ebert spheres, and it can be shown that they are unstable for certain values of n. Polytropic models, and thus the Lane-Emden equation, continue to be used down to the present when it is desired to incorporate a great deal of additional complex physics (for instance general relativity, dynamically important magnetic fields, or highly distorted shapes) into a stellar model. Acknowledgment The author wishes to acknowledge Corey Silbert of Simmons College for helping to compile some of this information. Selected References Bonnor, W. B. (1956). "Boyle's Law and Gravitational Instability." Monthly Notices of the Royal Astronomical Society 116: 351359. -- (1958). "Stability of Polytropic Gas Spheres." Monthly Notices of the Royal Astronomical Society 118: 523527. Emden, R. (1902). "Contributions to Solar Theory." Astrophysical Journal 15: 3859. -- (1907). Gaskugeln. Leipzig: B. G. Teubner. Empedocles of Acragas Katherine Bracher Whitman College, Walla Walla, WA, USA Born perhaps Acragas (Agrigento, Sicily, Italy), circa 493 BCE Died 433 BCE Empedocles, one of the followers of Parmenides in the Eleatic school of philosophers, is best known for his theory (later adopted by Aristotle)
Encke, Johann Franz
that everything in nature was composed of four as a professional astronomer thanks to Gauss'
elements, in varying amounts: earth, air, fire, and recommendation for a position as assistant at
water. Empedocles also hypothesized two opposing the Seeberg Observatory near Gotha. Having
forces, love and strife; the tension between these already published calculations of orbital elements
two produced cycles of change in the Universe. He of several of the newly discovered minor planets
may have realized that the Moon reflects sunlight as a student, Encke distinguished himself in
and travels around the Earth; he may also have his examination of the orbit of the third known
believed that the Moon caused eclipses of the Sun. short-period comet (2P/Encke), discovered in
In his cosmology the sky was an egg-shaped crystal November 1818 by Jean Pons and now called
surface with the stars attached; the planets moved Encke's comet (but not by Encke himself in his
freely. Empedocles was also a physician and gen- many publications). Restricted to the inner
erated some theories in medicine.
Solar System, with a period of only 3 years, the
orbit of Encke's comet changes constantly due
to the relatively large gravitational attraction of
the nearby planets, particularly Jupiter. To solve
this problem Encke devised a convenient mathe-
Empedocles (2001). The Poem of Empedocles. A text and translation with an introduction by Brad Inwood. Rev. ed. Toronto: University of Toronto
Press. Sarton, George (1927). Introduction to the History of Science. Vol. 1. Baltimore: Published for the
matical reduction of the series of differential equations
representing its perturbed orbital elements. Applied to a wide variety of objects with rel-
Carnegie Institution of Washington by Williams and atively perturbed orbits, Encke's method failed
completely, even when applied by a variety of
investigators in ever more sophisticated ways to
explain the complexities of motion of the comet.
Encke, Johann Franz
In the twentieth century it was shown that the orbit of this much-studied comet cannot be
Michael Meo Portland State University, Portland, OR, USA
explained by Newtonian laws alone, even assuming (as Encke and others did) motion in a resistive medium; the loss of mass due to outgassing has to
be taken into consideration.
Born Hamburg, (Germany), 23 September 1791 Died Spandau, (Berlin, Germany), 26 August 1865
Having made significant improvements in the instrumentation of the Seeberg Observatory, Encke was offered a membership in 1825 in the Berlin Academy of Sciences and the directorship
Johann Encke was the leading German astronomer of his generation, contributing substantially to celestial mechanics, observation of the Solar System, and the professional development of the German-speaking astronomical community. He was the son of Johann Michael Encke and Marie Misler. Educated at GoЁttingen University as a student of Carl Gauss, Encke, the eighth child of a Lutheran Pastor of Hamburg, began his career
of its observatory. Here he not only expanded the publication of its Berliner Astronomisches Jahrbuch and delivered well-attended lectures on astronomy at the request of the Ministry of Education, but also oversaw a substantial renovation of the observatory itself, including a new structure at a more appropriate suburban site and new, research-grade instruments, including a large Fraunhofer refractor. An ongoing project of the academy, now put under Encke's direction, was the preparation of accurate star charts. The
new instruments and the new charts were both
crucial in the short successful hunt for Neptune.
Michael Meo has retired.
In 1838, he discovered a gap in Saturn's rings
(between the A and F rings), later known as Encke's gap. Perhaps Encke's greatest triumph was the observation at the Berlin Observatory of the planet Neptune by his assistant Johann Galle the day after receipt of its predicted position calculated by Urbain Le Verrier, in contrast to more than 6 months of unsuccessful search at the Cambridge University Observatory and months of bureaucratic delay at the Paris Observatory. Instrumentation ordered and installed by Encke, accurate charts compiled under his direction, and observers he had trained all contributed to this signal accomplishment. In 1844 Encke received the recognition of appointment as professor of astronomy at the University of Berlin, the leading university in Prussia. Among his many influential students may be mentioned Benjamin Gould, Franz Brunnow, author of a leading astronomical textbook, Galle, and Giovanni Schiaparelli. A congenial man, Encke advised Friedrich Struve on how to equip a new observatory in Russia as early as 1820 and acknowledged in 1852 that George Bond, of Harvard College Observatory, had preceded him, in an application of perturbation theory. Encke retired as professor in 1863 but continued as director of the observatory until his death. Selected References Freiesleben, H. C. (1971). "Encke, Johann Franz." In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 4, pp. 369370. New York: Charles Scribner's Sons. Grosser, Morton (1962). The Discovery of Neptune. Cambridge, Massachusetts: Harvard University Press. Standage, Tom (2000). The Neptune File: A Story of Astronomical Rivalry and the Pioneers of Planet Hunting. New York: Walker and Co. Engel, Johannes Jurgen Hamel Universitat Landau, Landau in der Pfalz, Rheinland-Pfalz, Germany
Alternate Name Angelus Born Aichach, (Bavaria, Germany), probably 2 March 1453 Died Vienna, (Austria), 29 September 1512 As Georg Peurbach's successor, Johannes Engel strove to calculate new planetary tables. Engel began his studies in Vienna in 1468 as a pupil of Johann Muller (Regiomontanus). In August 1472, he registered at Ingolstadt, and became a master of arts in 1474. In 14891491, Engel worked in Augsburg as a proofreader for the printer Erhard Ratdolt, well known for the publication of numerous astronomical works (and previously active in Venice). In 1492, he returned to Ingolstadt and studied medicine. Until his death he earned his living as a doctor in Vienna, and was thus able to pursue his interests in astronomy and astrology. In his Almanach novum, Engel stated that in the Dominican monastery in Vienna there was a manuscript of Peurba, in which he noted that the traditional planetary theory, and both the Alphonsine and Bianchini's Tables, did not represent the motion of the planets with sufficient accuracy, but that this was common knowledge. When in Vienna, Engel established from his own observations that these differences, as well as those between his data and those given in Johannes StoЁffler's yearbook, amounted to about 13. This reveals Engels as a serious working astronomer who was aware of the deficiencies of contemporary astronomy. He also had at his disposal contemporary information regarding the works and projects of Muller, which are extremely valuable to us, because of the lack of reliable sources. Engels compiled numerous astrological calendars and yearly prognostications, the oldest of which is for 1484, and which appeared (partly) both in German and in Latin. His Opus Astrolabii plani in tabulis: a Johanne angeli liberalium magistro (1488) was a fundamental work for astrology. It contains numerous tables for astrological calculations (places of the Sun, the houses, temporal hours, and their astrological
Englefield, Henry Charles
characteristics, as well as 360 sample horoscopes, decorated with little images for locating the ascendant for each degree of any zodiacal sign). An edition of a number of works by the Islamic scholar AbuЇ Ma shar, De magnis conjunctionibus, that he had edited appeared in 1489, and was of great significance in the introduction of the astrological theory of conjunctions to later astrology.
Groningen professor Nicolaus Engelhard was a Copernican proponent in the Netherlands. Selected Reference Rienk, Vermij (2002). The Calvinist Copernicans: The Reception of the New Astronomy in the Dutch Republic, 15751750. Amsterdam: Koninklijke Nederlandse Akademie van Wetenschappen.
E Acknowledgements Translated by Storm Dunlop. Englefield, Henry Charles
Selected References AbuЇ, Mashar (1489). De magnis conjunctionibus, edited by Johannes Angelus. Augsburg: E. Ratdolt. Angelus, Johannes (1488). Astrolabium. Augsburg: E. Ratdolt. -- (1494). Astrolabium. Venice: J. Emerich. -- (1494). Ephemerides coelestium motuum usque ad annum 1500. Vienna: J. Winterburg. --. Vorhersage fuer 1496. "Dise Practica hat gemacht Mayster Johannes Engel in der loeblichen Universitet Ingelstatt", n.p. -- (1500). Libellus de calendarii emendatione. Vienna. -- (1502). Opus astrolabij plani in tabulis. Venice: L. Antonius. --. Almanach novum atque collectum . . . super anno domini 1510. Vienna: J. Winterburger, n.d. Bonatii, Guido (1491). Decem tractatus astronomiae, edited by Johannes Angelus. Augsburg: E. Ratdolt. Ferrari d'Occieppo, Konradin (1970). "Angelus (Engel), Johannes." In Dictionary of Scientific Biography, edited by Charles Couslton Gillispie. Vol. 1, pp. 165166. New York: Charles Scribner's Sons. Heitz, Paul and Konrad Haebler (1905). Hundert Kalender-Inkunabeln. Strasbourg, nos. 43, 62. Wickersheimer, E. (1928). "Note sur Johannes Engel (Angeli) d'Aichach, astrologue et meґdicin, mort a` Vienne en 1512." In Festschrift zur Feier seines 60. Geburtstages am 8. Dezember 1928 Max Neuburger gewidmet von Freunden, Kollegen und Schulern, pp. 316322. Vienna. Engelhard, Nicolaus Thomas Hockey Department of Earth Science, University of Northern Iowa, Cedar Falls, IA, USA Flourished The Netherlands, 1738
Luґis Tirapicos University of Lisbon, Lisbon, Portugal Born Sonning, Berkshire, England, 1752 Died London, England, 21 March 1822 Henry Charles Englefield was an antiquarian and amateur practitioner of zoology and geology. As an astronomer, he was the author of books regarding the determination of the orbits of comets and also observed variable stars. He made improvements in optical as well as other kinds of scientific instruments. Englefield was the eldest of the five children of Sir Henry Englefield, by his second wife, Catharine. He succeeded his father in the baronetage in May 1780, but the title became extinct since Henry Charles did not marry. He was elected a fellow of the Royal Society in 1778 and a fellow of the Society of Antiquarians the following year. Under his direction, between 1797 and 1813, the Society of Antiquarians published a series of engravings of English churches and cathedrals. Englefield became president of the Society in the period 18111812. Englefield was also a fellow of the Linnean Society and joined the Dilettanti Society in 1781, where he was its secretary for 14 years. His Discovery of a Lake from Madder received the gold medal of the Society of Arts. In 1784, Englefield contributed observations of the variable star Algol (b Persei) to the Royal Society (published in the Philosophical Transactions) using an "excellent night-glass,
Ensor, George Edmund
magnifying about eight times, with a field of 5." In the 1780s and 1790s, he also communicated new observations of variable stars by John Goodricke and Edward Pigott the noted pioneers and discoverers of the periodic variation in brightness of these celestial objects. However, Englefield's most significant contributions to astronomy were probably his computations of the orbits of comets. In 1788, he published the apparent places of comet 153P/1661 C1(Ikeya-Zhang) that was expected during its return the following year. He did so before knowing that French astronomer Alexandre Guy Pingreґ had prepared the same sort of tables for publication in the Connaissance des Temps (1789). At any rate, he justified his publication by arguing that his tables were "much more copious than those of Mr. Pingreґ." In the final pages of his small book, he also proposed a method of taking the differences of right ascension and declination with James Bradley's reticule rhomboide. This new method did not require the placement of the instrument in the plane of the equator. A more extensive work on comets was published in 1793, Englefield's On the Determination of the Orbits of Comets. In this treatise, he expressed regrets that in all countries of the European continent, mathematicians and astronomers had tried to improve and simplify the computation of the orbits of comets, but in England, "since the decease of Dr. Halley, nothing has been published on this subject worthy of mention, except the little treatise of Mr. Barker." Englefield's treatise was based on the methods of Rudyer Boskovic and Pierre-Simon de Laplace and included worked examples. Around 1808, Englefield invented a portable mountain barometer that was constructed by Thomas Jones and, 3 years later, proposed new improvements in the cistern (containing mercury) of the instrument.
Englefield, Henry Charles (1784)."An Observation of the Variation of Light in the Star Algol. In a Letter from Sir Henry C. Englefield, Bart. F. R. S. and S. A. to Joseph Planta, Esq. Sec. R. S." Philosophical Transactions of the Royal Society of London 74: 13. -- (1788). Tables of the apparent places of the Comet of 1661, whose return is expected in 1789. London: Peter Elmsly. -- (1793). On the Determination of the Orbits of Comets. London: Peter Elmsly. Ensor, George Edmund Thomas R. Williams Rice University, Houston, TX, USA Born New Zealand, 1873 Died Pretoria, South Africa, 8 June 1943 A radiographer by profession, George Ensor's main avocational interest was in variable star astronomy. Ensor arrived in South Africa as part of a contingent from New Zealand in connection with the South African War and remained there after the war was over. He served as the director of the Astronomical Society of South Africa's [ASSA] variable star section and submitted nearly 15,000 observations to the American Association of Variable Star Observers during the period 19261940. Ensor was also an active lunar occultation observer for the Greenwich Observatory. He discovered comet C/1925 X1 and shared the discovery of comet C/1932 G1 with another South African amateur, Hendon Edgerton Houghton. His reputation in astronomy was such that Astronomer Royal Frank Dyson consulted him on possible sites for the Radcliffe Observatory, which was ultimately located within a few meters of the site recommended by Ensor.
Nurse, Bernard (2004). "Englefield, Sir Henry Charles." In Oxford Dictionary of National Biography, edited by H. C. G. Matthew and Brian Harrison, vol. 18, pp. 449450. Oxford: Oxford University Press.
Selected Reference Anon. (1943). "Obituary". Monthly Notes of the Astronomical Society of Southern Africa 11, no. 7: 45.
Epicurus of Samos
Epicurus was an atomist. According to
atomism, which was first proposed by
Leucippus and Democritus, everything in
the world is made up of atoms, uncuttable bits of
Department of Earth Science, University of
matter, moving through empty space, and every-
Northern Iowa, Cedar Falls, IA, USA
thing in the Universe can be explained in terms of
the mechanical interaction of these atoms. In his
ethics, Epicurus preached that the point of life is
Flourished Cyme (near Izmir, Turkey), fourth to gain tranquility for oneself and that the fear of
the gods and of an unpleasant afterlife destroys
In 372 BCE, Greek historian Ephorus reported Epicurus insisted that all terrestrial and
seeing a comet break into two. It has been celestial phenomena are nothing more than the
speculated that this comet is the ancestor of result of the motions, reboundings, and entangle-
Carl Kreutz's sun-grazing comets.
ments of various types of atoms. Explanations of
these phenomena in such mechanistic terms,
Epicurus thought, should displace explanations
that appeal to the will of the gods. Epicureans
opposed divination and astrology, since the
Barber, G. L. (1979). The Historian Ephorus. New York: movements of the heavens do not reveal any
sort of divine plan and belief in divine providence
and divine interference breeds anxiety. Epicurus
was directing his attack both against the popular
Epicurus of Samos
Olympian religion and against the cosmologies of
philosophers like Plato, who said that the gods
are responsible for the orderly motions of theUniversity of Minnesota
Epicurus believed that there are an infinite
number of atoms, which have existed for an eter-
nity of time, moving through an infinite expanse
Born Samos (Greece), circa 341 BCE
of space. Because of this, ours is only one out of
Died Athens (Greece), circa 271 BCE
an infinite number of worlds, and our world is not
at the center of the cosmos, since there is no
Epicurus based his astronomy on his general center. Since an infinite number of worlds exist,
metaphysical views and put it in the service of there must be life on other planets, including
intelligent life. Although the Universe as
Epicurus was born in the Athenian colony of a whole is eternal, our particular cosmos, which
Samos, an island in the Mediterranean Sea. He is a chance conglomeration of atoms, has
founded the Garden, which was a combination of a beginning in time and will eventually fall apart.
philosophical school and community, around In all of these doctrines, except concerning
306 BCE in Athens. Epicurus died from kidney the eternity of the Universe, Epicurus opposed
stones. He had no descendants, but the the views of Aristotle. Aristotle promulgated
Garden continued as a thriving philosophical a geocentric view of the Universe and believed
community for centuries after Epicurus' death, that this cosmos (the Earth, Sun, planets,
and Epicureanism became one of the major and stars) is eternal and spatially limited.
philosophical systems in the Greco-Roman Aristotle's cosmology became the Church's offi-
world, competing with Stoicism for people's cial cosmology in the Middle Ages
, but during
the Renaissance and because of early modern
reaction against scholastic neo-Aristotelianism, interest in Epicurus' astronomy was revived, particularly by the French philosopher Pierre Gassendi. Even though he thought that mechanistic explanations of astronomical phenomena are necessary in order to dispel our fear of godly meddling, Epicurus believed that natural science has no value in itself. Epicurus offered atomistic and naturalistic explanations for a wide range of celestial and meteorological phenomena, but his particular explanations are largely ad hoc speculations and did little to advance astronomy. Epicurus said that in many cases a phenomenon may permit multiple explanations, and that we must take care not to rule out any possible explanation too hastily. Epicurus followed his own method, enumerating many possible explanations for various phenomena. For instance, Epicurus said that solar and lunar eclipses could be caused either by the extinguishing of their light or because their light is blocked by another body, and he listed four different explanations of thunder in terms of atomic motions. Most of Epicurus' own writings are lost, but the main outlines of his philosophy are contained in three of his letters: the Letter to Pythocles, which summarizes his explanations for celestial and meteorological phenomena; the Letter to Menoeceus, which summarizes his ethics; and the Letter to Herodotus, which summarizes his metaphysics. Epicurus' arguments for an infinite number of worlds, the absence of divine intervention in the world, and the doctrine of multiple explanations can be found in the Letter to Herodotus sections 45 and 7380. All three letters are preserved by the ancient biographer and gossip, Diogenes Laertius, in Book ten of his Lives of the Philosophers. Epicurus' own writing is often compressed and unclear. The Latin poet Lucretius, however, penned De Rerum Natura, a masterful exposition in hexameter of Epicurus' metaphysics, philosophy of mind, and natural science. The end of Book II gives the Epicurean argument for an infinite number of worlds and explicitly states that there are many worlds in which people and nonhuman animals exist. The first half of
Book V contains the Epicurean arguments that the processes of the Universe occur for no divine purpose, and that the world is not eternal. Books V and VI contain Epicurean explanations for various astronomical and meteorological phenomena. Selected References Anon. (1994). The Epicurus Reader: Selected Writings and Testimonia, translated and edited by Brad Inwood and L. P. Gerson. Indianapolis: Hackett. Asmis, Elizabeth (1984). Epicurus' Scientific Method. Ithaca, New York: Cornell University Press. Avotins, Ivars (1983). "On Some Epicurean and Lucretian Arguments for the Infinity of the Universe." Classical Quarterly, n.s., 33: 421427. Diogenes, Laertius (1925). Lives of Eminent Philosophers, translated by R. D. Hicks. Loeb Classical Library, no. 184. Cambridge, Massachusetts: Harvard University Press. Long, A. A (1977). "Chance and Natural Law in Epicureanism." Phronesis 22: 6388. (For Epicurus' mechanistic cosmology.) -- (1986). Hellenistic Philosophy: Stoics, Epicureans, Sceptics. 2nd ed. Berkeley: University of California Press. Lucretius (1968). The Way Things Are: The De Rerum Natura of Titus Lucretius Carus, translated by Rolfe Humphries. Bloomington: Indiana University
Press. Solmsen, Friedrich (1951). "Epicurus and Cosmological Heresies." American Journal of Philology 72: 123. Epping, Joseph Thomas Hockey Department of Earth Science, University of Northern Iowa, Cedar Falls, IA, USA Born Neuenkirchen, (Schleswig-Holstein, Germany), 1835 Died Exaeten, The Netherlands, 1894 Joseph Epping joined the Society of Jesus in 1859. He was ordained a priest in 1870. In 1872 Epping followed the call of Ecuadorian President Garcia Moreno to establish a university in Quito. He taught mathematics there until forced out after
Eratosthenes of Cyrene
the assassination of Moreno. Epping arrived in There are very few remains of Erastosthenes'
Holland in 1876; he spent the rest of his life in epic poem Hermes and of his elegy Erigone. His
Blijenbeck and Exaeten. In Exaeten he published 12 books on ancient Attic comedy have been lost.
Der Kreislauf im Kosmos (1882), a criticism The extant book Katasterismos (Star arrange-
of the Immanuel Kant/ Pierre-Simon ments), which explains the mythological origin
Laplace "Nebular Hypothesis" for the origin of of the names of the constellations, is presumably
the Solar System.
an ancient abridgment of the work he wrote on the
As Assyriologist Johann Strassmaier, S. J., subject. According to R. Pfeiffer, Eratosthenes
studied Babylonian cuneiform tablet inscriptions was the founder of critical chronology. In his lost
from the British Museum, he realized that he Chronographi (Chronographies), he gave a full
needed help in interpreting the extensive writings chronological survey of Greek history from the
therein on astronomy. Strassmaier recruited fall of Troy to the death of Alexander, based on
Epping. Together they published the landmark the lists of Spartan kings and of Olympian victors.
Astronomisches aus Babylon (1889).
His precise reconstruction of the latter list,
Olumpionikai (Olympian victories), is also lost.
Eratosthenes' contributions to mathematics
included research on the duplication of the cube,
and the famous sieve. The "sieve of Eratosthenes"
Aaboe, A. (2001). Episodes from the Early History of was, until the recent invention of advanced
Astronomy. New York: Springer.
computer programs, the only algorithm available
for finding prime numbers. To find all primes
smaller than a given integer N we write down the
first N positive integers in order. We start then
Eratosthenes of Cyrene
a sequence of operations, in each of which we
cross out one or more integers, without deleting
them. In the first operation, we cross out one,
Universidad Diego Portales, Santiago, Chile
which is not a prime. The first uncrossed integer
is then the first prime, namely two; we leave it
untouched and cross out every second integer
Born Cyrene (near Darnah, Libya),
from then on. After the second operation, the first
circa 274 BCE
uncrossed integer is the second prime, namely
Died Alexandria, (Egypt), circa 194 BCE
three; we leave it untouched and cross out every
third integer from then on. (Some integers, like six
Eratosthenes, Greek scholar, scientist, and math- and 12, will then be crossed out more than once.)
ematician, is chiefly remembered for devising And so on. . . After the nth operation, the first
and performing the first measurement of the uncrossed integer is the nth prime, which we
circumference of the Earth, and for inventing denote by p(n). We leave it untouched and cross
the algorithm known as the sieve of Eratosthenes. out every p(n)th integer from then on. The proce-
According to the Suda Eratosthenes was born dure stops as soon as the first uncrossed integer is
in the 126th Olympiad (276/273 BCE), but this is greater than the square root of N (e. g., after the
hard to reconcile with Strabo's assertion that he 12th operation, if N ј 1,000). At that stage, every
studied in Athens with Zeno the Stoic, who died uncrossed item in the list is a prime number N.
in 262/261 BCE. Around 246 BCE, Eratosthenes Eratosthenes' method for measuring the
moved to Alexandria where he succeeded circumference of the Earth is reported by
Apollonius as chief librarian. We are told he Cleomedes. It rests on two idealizing
lived to be 80. According to the Suda, the next assumptions: (1) The Earth is a perfect sphere
chief librarian, Aristophanes of Byzantium, was and (2) the Sun is so far away that light coming
also his pupil.
from it reaches the surface of the Earth along
parallel lines. Moreover, Eratosthenes incorrectly assumed (3) that Alexandria and Syene (today's Aswan) lie on the same meridian. On the summer solstice a pole planted vertically on the ground at Syene throws no shadow at noon. At Alexandria, on that same noon, a pole of the same height h similarly planted on the ground, makes a shadow of length l. From the ratio h:l Eratosthenes could figure out the size of the angle a made by the vertical pole and the direction from which solar light fell on it in Alexandria. By assumptions (2) and (3) this direction is parallel to the direction of the solar light falling at that moment on Syene; hence, by assumption (1), angle a is equal to the difference in latitude between Syene and Alexandria. If Syene and Alexandria both lie on the same great circle of a sphere of circumference equal to K, if D is the length of arc between them, and if the angle a subtended by this arc is expressed in degrees, then, evidently,
According to Cleomedes, Eratosthenes's calculations yielded K ј 250,000 stadia. The quality of Eratosthenes' estimate depends of course on the actual length of one stadion. In classical Greece, it measured exactly 600 ft. The length of a foot varied from one city-state to another, but not by much, and Tannery suggests one stadion ј 185 Ж 5 m. Then, K ј 46,250 km, a fair estimate of the circumference of the Earth. However, Pliny says that Eratosthenes counted 40 stadia per schoenus, an Egyptian unit that we know was equal to 630 km. Using this equivalence, we get K ј 39,375 km, a figure eerily close to the actual length of a terrestrial meridian (%39,942 km).
Cleomedes (1891). De motu circulari corporum caelestium libri duo, edited by H. Ziegler. Leipzig: Teubner, pp. 95100. Dreyer, J. L. E. (1906). History of the Planetary Systems from Thales to Kepler. (Revised, with a foreword by W. H. Stahl, as A History of Astronomy from Thales to Kepler. New York: Dover, 1953, pp. 175178.) Eratosthenes (1822). Eratosthenica, edited by G. Bernardy. Berlin: Reimer. (Reprint, Osnabruck: Biblio Verlag, 1968.) -- (1822). Die geographischen Fragmente des Eratosthenes, edited by Hugo Berger. Leipzig: Teubner. (Reprint, Amsterdam: Meridian, 1964.) -- (1925). "Fragmenta." In Collectanea Alexandrina, edited by J. U. Powell. Oxford: Oxford University Press. -- (1938). "Fragmenta." In Supplementum Hellenisticum, edited by H. Lloyd-Jones and P. Parsons, pp. 183186. Berlin: W. de Gruyter. Heath, Sir Thomas L. (1913). Aristarchos of Samos, the Ancient Copernicus. Oxford: Clarendon Press. (Reprint, New York: Dover, 1981, pp. 339341.) Pfeiffer, Rudolf (1968). History of Classical Scholarship from the Beginnings to the End of the Hellenistic Age. Oxford: Clarendon Press pp. 152170. Pliny (19061909). C. Plini Secundi Naturalis historiae libri XXXVII, edited by C. Mayhoff. Leipzig: Teubner, Bk. 12, }53. Strabo (1877). Strabonis geographica, edited by A. Meinecke. Leipzig: Teubner. (Reprint, Graz: Akademische Druck- und Verlagsanstalt, 1969.) Tannery, Paul (1895). Recherches sur l'histoire de l'astronomie ancienne. Meґmoires de la Socieґteґ des Sciences Physiques et Naturelles de Bordeaux, 4th. ed. seґr., 1 Paris: Gauthier-Villars. (Reprint, Paris: Jacques Gabay, 1995, pp. 103121.) Tosi, Renzo (1998). "Eratosthenes." In Der neue Pauly: Enzyklopadie der Antike, edited by Hubert Cancik and Helmuth Schneider. Vol. 4, cols. 4447. Stuttgart: J. B. Metzler. Wolfer, Ernst Paul (1954). Eratosthenes von Kyrene als Mathematiker und Philosoph. Groningen: WoltersNoordhoff. Ericsson, John Thomas Hockey Department of Earth Science, University of Northern Iowa, Cedar Falls, IA, USA
Anon. (1897). Pseudo-Eratosthenis Catasterismi, edited by A. Olivieri. Mytographi Graeci. Vol. 3. Leipzig: Teubner. Anon. (19281971). Suda. Suidae lexicon, edited by A. Adler. Lexicographi Graeci. Vol. 1. Leipzig: Teubner. (See 1.11.4, letter E, entry 2898.)
Born Langbanshyttan, Varmland, Sweden, 31 July 1803 Died New York, New York
, USA, 8 March 1889
Esclangon, Ernest Benjamin
Engineer John Ericsson invented the screw A 24/31-in. Schmidt telescope, with optics
propeller for ships and built the first ironclad supplied by the Perkin-Elmer Corporation and
warship, U. S. S. Monitor. He was a contrarian mounting furnished by Harvard, was installed.
when it came to the Moon, though. Ericsson Erro remained as director of OAT until his
wrote that the lunar craters were not the product retirement in 1950; he was succeeded by
of volcanism, as was popularly thought. Instead, Guillermo Haro.
he envisioned the Moon as a cold world and the Erro wrote El pensamiento matemaґtico
craters as the product of "annual glaciers."
contemporaґneo (Contemporary mathematical
thought, 1944), and one novel, Los pies descalzos
(Bare feet, 1951), which reflected his social
opinions and broad personality. His country's
first major planetarium, which was opened in
Church, W. C. (1890). The Life of John Ericsson. Meґxico City in 1967, was named for Erro. New York: C. Scribner's Sons.
Erro, Luis Enrique Jordan D. Marcheґ II University of Wisconsin, Madison, WI, USA Born Mexico City, Mexico, 6 January 1897 Died Mexico City, Mexico, 18 January 1955
Freire, Silka (1992). "Erro, Luis Enrique (18971955)." In Dictionary of Mexican Literature, edited by Eladio Corteґs, pp. 212213. Westport, Connecticut: Greenwood. Torres-Peimbert, Silvia 1999. "A Century of Astronomy in Meґxico: Collaboration with American Astronomers." In The American Astronomical Society's First Century, edited by David H. DeVorkin, pp. 7483. Washington, DC: Published for the American Astronomical Society through the American Institute of Physics.
Diplomat and amateur astronomer Luis Enrique Erro was educated at Morelia, Michoacaґn, before he pursued eclectic studies in mathematics, civil engineering, history, and law. An outstanding public speaker, Erro first settled into business and political activities. Exiled from Mexico in 1923, he later returned as a director of technical education and was appointed an advisor to the Mexican presidency. Erro became enamored of amateur astronomy and specialized in the study of southern variable stars. In the late 1930s, Erro served at first secretary of the Mexican Embassy at Washington, District of Columbia, where he came into contact with the American Association of Variable Star Observers (AAVSO), and the Harvard College Observatory. Erro convinced Mexican President Manuel Aґ vila Camacho to provide support for a modern astrophysical observatory in his native land. Construction of the Observatorio Astrofґisico de Tonantzintla (OAT) at Puebla began in 1941; the facility was dedicated on 17 February 1942.
Erwin Finlay-Freundlich Freundlich, Erwin Esclangon, Ernest Benjamin Jacques Leґvy Paris, France Born Mison, Alpes-de Haute-Provence, France, 17 March 1876 Died Eyrenville, Dordogne, France, 28 January 1954 Ernest Esclangon is often remembered for his contributions to applied physics during World Jacques Leґvy: deceased.
Esclangon, Ernest Benjamin
War I and for his automated distribution of time signals by telephone. Esclangon began his studies in a colle`ge (school) in Manosque, his brother being a schoolmaster. He later attended the lyceґe (academy) in Nice before entering the Eґ cole Normale Supeґrieure in Paris (1895). He received his degree in mathematics and secured a position at the Bordeaux Observatory in 1899 under Georges Rayet, which decided the fate of his career. There, Esclangon served as aide-astronome and astronom-adjoint. While in Bordeaux, he taught courses in rational mechanics as well as in differential calculus. In 1919, Esclangon became director of the Strasbourg Observatory. With help from Andreґ Danjon, he revived the institution in the postwar period. Esclangon then succeeded Henri Deslandres as director of the Paris Observatory in 1929, a position he held until his retirement in 1944. At both Strasbourg and Paris, he was simultaneously a professor of astronomy in the cities' universities. His teaching abilities were much appreciated by his students, and Esclangon remained open to new ideas. The first research work performed by Esclangon was his doctoral dissertation (1904), which examined quasiperiodic functions. Introduced in 1893 by mathematician Piers Bohl, these functions proved particularly powerful in the case of Fourier series, producing a limited number of terms in their application. Esclangon perfected their theory, studied the corresponding differential equations, and established their usage in mathematical physics. This work constituted his main contribution to pure science, for which he was awarded the Grand Prix of the Acadeґmie des sciences. Esclangon was also fond of the practical uses of mathematics, and his reputation was enhanced in two very different fields. Soon after World War I began, Esclangon proposed to the Service Geґographique de l'Armeґe his idea of pinpointing the enemy's location by triangulating the sounds of artillery firings. Through field experimentation, Esclangon successfully constructed equipment that performed this task. General Ludendorff, head of the German staff
officers, later argued in his memoirs that Esclangon's defensive device was one of the keys behind the victory of the allied troops. At the Paris Observatory, Esclangon responded creatively to an increasing demand from citizens to obtain the proper time by telephone. He created the first "talking" (i.e., automatic self-announcing) clock. Esclangon broadcasts the time through a series of photoelectric cells, which activated pistes sonores located on a rotating cylinder. The corresponding "blips" were issued from a synchronous clock, driven in turn by a fundamental clock at the observatory. The time service was inaugurated on 14 February 1933, and immediately the number of calls jumped to more than several thousand per day. The accuracy of the time provided on the telephone was better than 0.1 s. During his lifetime, Esclangon published more than 200 papers on a variety of subjects, which included the mechanics of flight, acoustics, and relativity theory. Most of his publications were related to positional astronomy, instrumentation, and chronometry. Esclangon's last paper investigated the orbital mechanics of an artificial Earth satellite, several years before the Sputnik satellite was launched by the Soviet Union
. Esclangon's mathematical and scientific skills were called upon by various administrative agencies
. His wartime contributions led to appointments as an attacheґ in the cabinet of the minister of the navy, along with an artillery commission. He later became a member of the Commission des inventions for the Centre National de la Recherche Scientifique. Esclangon was elected to the Acadeґmie des sciences in 1929 and to the Bureau des longitudes in 1932. He was made a Commandeur de la Leґgion d'honneur. Esclangon was elected president of the International Astronomical Union (19351938) following his organizing of its general assembly in Paris, and its participants were addressed by the President of France. Esclangon lived in the village Eyrenville, where he owned a house in which he installed a water mill to provide electricity. He rode an old bicycle, which made such a noise that the citizens
Espin, Thomas Henry Espinall Compton
were preinformed of his arrival. They much Espin continued to work with Celestial Objects
appreciated Esclangon's kindness, simplicity, after Webb's death, and eventually published
and the accuracy of his weather forecasts.
a reedited and enlarged two-volume fifth edition
(1893; reprinted 1905) of Webb's original book,
which by then had become a standard work for
amateur astronomers. In 1917 Espin updated
a sixth edition of Celestial Objects.
Danjon, A. (1955). "Ernest Esclangon." Monthly Notices
Espin examined the stars listed in the Bonner
of the Royal Astronomical Society 115: 124.
Durchmustrung (Bonn survey) with
a spectroscope of his own design using his large
telescopes. With this approach it was possible to
more reliably detect those stars with redder than
Espin, Thomas Henry Espinall
normal colors. Espin gathered observations for
a total of 3,800 red stars into several catalogs
following the earlier examples of Thomas
Thomas R. Williams
Backhouse and John Birmingham. In 1890,
Rice University, Houston, TX, USA
having carefully verified the colors given by
others and after adding his own discoveries,
Espin published the results as a sixth edition of
Born Birmingham, England, 28 May 1858
Birmingham's catalog of red stars. The stars
Died Tow Law, Durham, England,
included in Espin's catalogs were generally too
2 December 1934
faint to appear in the Harvard catalogs of spectra,
which added to the value of his work. Espin also
Using 17- and 24-in. reflecting telescopes, the recognized that many of the red stars he was
Reverend Thomas Espin discovered and mea- cataloguing were variable; he is credited with
sured 2,575 double stars and prepared catalogs the discovery of more than 30 new variable
of 3,800 red stars classified on the basis of his stars. The most noteworthy of his variable star
spectroscopic examination. As the son of Rever- discoveries was Nova Lacertae, discovered in
end Thomas Espinell and Elizabeth (neґe Jessop) 1910. In his extensive survey, Espin measured
Espin, he enjoyed a privileged childhood, was and recorded the positions of 2,575 pairs of
educated at Oxford, and entered the ministry of close stars.
the Church of England. In 1888, at 33 years of With Webb as a mentor, a solid observing
age, he became Vicar of Tow Law, a position he program, and an aggressive effort to publish his
held as a single clergyman for the remainder of results in the English Mechanic, it should be no
his life. His scientific interests were broad, in surprise that Espin was well known as an amateur
common with many clergymen of his time, but astronomer. He was an active participant in sev-
his strongest interest was astronomy.
eral efforts to organize amateur astronomers in
The appearance of comet C/1874 H1 (Coggia) England. When the Liverpool Astronomical
in April 1874 stimulated Espin's earliest efforts Society [LAS] was formed in 1881,
in observational astronomy. It was not long after Espin became an active member, along with
the event that he began contributing regular arti- Isaac Roberts, William Denning, Webb,
cles, signed T.E.E., to The English Mechanic, Thomas Elger, and other well-known ama-
a practice he continued for most of his active teurs from the region. Espin was the second
career. At about the same time, the Prebendary LAS president (1884/1885). When the LAS lead-
Thomas Webb solicited Espin's help in gath- ership recognized that overly enthusiastic mem-
ering and editing information for a revision of bers were reporting spurious observations as
Webb's Celestial Objects for Common Tele- "discoveries," Espin volunteered to make
scopes, an honor for the young observer. confirming observations on short notice.
Eґtable de la Brie`re, Nicole-Reine
However, his efforts led to conflicts over his methods of making attributions of the discovery priority and to other problems. When LAS ultimately failed, Espin became an active member of the British Astronomical Association. Espin was a fellow of the Royal Astronomical Society. In 1913, he received its Jackson-Gwilt Medal for his discoveries of double stars and catalog of red stars as well as his Nova Lacertae discovery. He was elected to the International Astronomical Union Commission on Double Stars. Selected References Anon. (1935). "Death of Mr. Espin." Publications of the Astronomical, Society of the Pacific 47: 6465. Gilligan, Gerard (1996). The History of the Liverpool Astronomical Society. Privately published. Tow Law, Local History Group (1992). The Star Gazer of Tow Law. Privately published. W.M. (1935). "The Rev. T. H. E. C. Espin." Observatory 58: 2729.
Asia. One reference indicates that Euctemon was wealthy enough to have craftsmen working for him. Euctemon's chief astronomical contributions were largely in conjunction with those of Meton. They were reported to have developed a calendar of 365.25 + 1/76 of a day (30 min too long). A 19year cycle was developed from an observation of the solstices since it was similar to observations made earlier in Mesopotamia, although the independent nature of the discovery is suspect. The Metonic cycle arises from 19 solar years, being almost exactly equal to 235 lunar cycles, and allows the prediction of eclipses. They also noted the inequality in the lengths of the seasons. Euctemon and Meton are also known for having introduced the parapegma, which was a tool used to associate the rising of a particular star and the civil calendar date. The parapegma was a stone tablet with movable pegs and inscriptions that allowed for such a calculation. A crater on the Moon is named for Euctemon.
Eґ table de la Brie` re, Nicole-Reine Lepaute, Nicole-Reine Euctemon Ian T. Durham Saint Anselm College, Manchester, NH, USA
Selected References Jones, A. H. M. (1955). "The Social Structure of Athens in the Fourth Century B.C." Economic History Review 8: 141155. Smith, David Eugene (1958). History of Mathematics. Vol. 1. Boston: Ginn and Co., 1923; New York: Dover. Steel, Duncan (1999). Eclipse: The Celestial Phenomenon Which Changed the Course of History. London: Headline Book Publishing.
Flourished (Greece), circa 432 BCE
Eudemus of Rhodes
Almost nothing is known of the Greek astronomer Euctemon, including his birth and death dates; it is known that he worked with the astronomer Meton in Athens around 432 BCE. This bit of information comes to us from Ptolemy, who mentions Meton and Euctemon. There is also a reference to Euctemon in Pausanius' Description of Greece as being the father of Damon and Philogenes, two Athenians who provided ships to the Ionians for their voyage to
Thomas Hockey Department of Earth Science, University of Northern Iowa, Cedar Falls, IA, USA Flourished (Greece), fourth century BCE Eudemus was a student of Aristotle and an associate of Theophrastus. Like Theophrastus, he wrote a history of astronomy.
treated the 8-year cycle of the calendar, over
Bodnaґr, Istvaґn, and William W. Fortenbaugh (2002). Eudemus of Rhodes. New Brunswick, New Jersey: Transaction Publishers.
which he perhaps distributed 49 months of 30 days and 50 months of 29 days in eight Egyptian 365-day years. He is reported to have set the interval between autumnal equinox and winter
solstice as 92 days and that from winter solstice
to spring equinox as 91 days; the other two inter-
vals are not known but must sum to 182 days, and
both were most likely 91 days (since Eudoxus
Paul T. Keyser
later assumed uniform solar motion). This
means that he ignored the earlier work of
Cornell University, Ithaca, NY, USA
Euctemon and Meton on the inequality of
the seasons and on the 19-year lunisolar cycle.
Eudoxus also gave seasonal weather and star-
Born Knidos (Tekir, Turkey), circa 390 BCE appearance data, preserved in the calendar
Died Knidos (Tekir, Turkey), circa 338 BCE appended to Geminus. It may also be at this
time that he wrote Disappearances, which appar-
Eudoxus offered the first fully worked-out model ently treated the seasonal visibilities of stars.
of planetary motion.
Eudoxus seems to have been the first to estimate
Eudoxus was the son of Aiskhines of Knidos; the relative size of the Sun as many times larger
he was probably born about 390 BCE, when than the Moon. ( Archimedes records that he
Knidos was a Spartan ally and a closed oligarchy. said "nine.")
Eudoxus was married and had three daughters, Eudoxus visited Mausolus of Halikarnassos
Aktis, Delphis, and Philtis; he died at the (modern Bodrum) around 364/363 BCE and
age of 52.
probably also visited his birthplace at this time.
Eudoxus studied mathematics under Knidos had relocated its site (from modern Datcёa
Archytas of Taras and medicine under to the better harbor at modern Tekir) around
Philistion of Lokroi in southern Italy. He made 365360 BCE and changed its constitution from
astronomical observations there and in Sicily oligarchic to democratic. Strabo records that
perhaps around 361/360 BCE when he may Poseidonius claimed to have seen an observatory
have been in Sicily.
used by Eudoxus in new Knidos, but excavators
Diogenes reports that Eudoxus came to Athens have not identified it.
with little money at age 23, with his patron doctor Then, around 363357 BCE, Eudoxus taught
Theomedon; he lived in the port, Piraeus, for at Cyzicus (modern Belkis), where his students
2 months, walking up to Athens daily for lectures included the mathematician brothers
at the academy. Around 366/365 BCE he sailed Menaechmus and Dinostratus of Prokonessos
from Knidos to Egypt with Chrysippus, intro- and three natives of Cyzicus: Athenaeus (not the
duced by a letter from Agesilaus II of Sparta to much later mechanician), Polemarchus (the
Pharaoh Nectanebo I. For over 1 year, Eudoxus astronomer and teacher of Callippus), and per-
remained in Heliopolis, near Cairo, studying lan- haps Helicon. Besides mathematics and
guage and religion with the priest Cho-nouphis astronomy, he taught geography, metaphysics,
and making astronomical observations at nearby and ethics. Probably during this period, Eudoxus
Kerkesoura. He also visited Memphis, where the composed his Survey of Earth, the astronomical
priests predicted that his life would be short but works Mirror and Phainomena, as well as a work
Geminus reports that Eudoxus wrote on the Eudoxus's geography was the earliest to
calendar, and some sources state that he wrote an employ mathematical methods and the spherical
Octaeteris (probably circa 365/364 BCE), which Earth model. He covered "Asia" (the East),
including Egypt, in Books 13, and "Europe" (the West), including Libya, in Books 46, with Islands (including Sicily and its Pythagoreans) in Book 7, telling ethnographic stories similar to those of Herodotus. He may be the author of the earliest extant estimate of the circumference of the Earth, 40 myriad stades (approximately 75,000 km), in Aristotle's On Heaven. The two works of descriptive astronomy, almost identical according to Hipparchus, were apparently based on observations made from a latitude where the longest day was about 15 h (about 42 20 N), probably Cyzicus. They were the earliest systematic analysis of the sky, describing the constellations located along the celestial circles. Eudoxus's work was the foundation of Aratus's poem Phainomena and is described in Hipparchus's commentary thereon. Eudoxus located stars relative to parts of their figures and sometimes clarified placements with geometry. He placed the solstitial and equinoctial points at the middle of the constellations Aries, Cancer, Libra, and Capricorn, possibly following the similar Babylonian practice, but he rejected their claims of predictive astrology. Vitruvius credits him with the invention of a type of sundial called the arachne^ ("spider[-web]"). Eudoxus's mathematical work developed the theory of proportion presented in Euclid, Books 5 and 6, and the method of "exhaustion" (approach to the limit) presented in Euclid, Book 12. The former provided a definition of proportion applicable both to rational and irrational numbers (which D. Fowler suggests arose from his calendaric work); the latter provided a means to prove formulae for the area or volume of figures not tractable by Greek geometrical methods, such as the volume of the cone or pyramid. Some years before 348 BCE, Eudoxus returned to Athens, accompanied by many students, and continued his research and teaching. (He did not join the academy.) He published his greatest astronomical contribution, the theory of concentric spheres, in On Speeds, probably after Plato's death, perhaps about 345340 BCE. Attempts to reconstruct the lost work are rife with ambiguity, because we depend entirely on
a brief report in Aristotle's Metaphysics and a longer report in Simplicius that depends on the lost work On Counter-rotating Spheres of the second-century astronomer Sosigenes, itself dependent on Eudemus's lost History of Astronomy, Book 2. Eudoxus's books may not have survived the Roman conquest of Egypt. The theory was a geocentric model of planetary motion, attempting to explain the movements of the seven planets (Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn) on a common basis. Although probably not predictive, it contained numerical parameters based on observation. Each of the seven planets had three or four concentric rotating spheres whose axes were tilted with respect to one another and whose compound motions explained the observed motion of the respective planet. The outermost sphere of each planet moved with the same rotational velocity as the sphere of the fixed stars, i.e., with a 1-day period, rotating from east to west. The second sphere rotated with its equator in the plane bisecting the band of the zodiac, from west to east, with "zodiacal" periods preserved by Simplicius (corresponding modern periods are given in the third column):
Saturn Jupiter Mars
30 years 12 years 2 years
29.45 years 11.86 years 1.88 years
(The periods of Venus and Mercury are not comparable.) The Sun and Moon each had one more sphere, which rotated very slowly (the solar one east to west and the lunar west to east), with its equator sufficiently inclined to the center of the band of the zodiac to explain the deviation of the Sun or Moon from that circle. Modern scholars usually suggest that Eudoxus must have intended a period of 1 month for the third lunar sphere, the second sphere being the very slow one (period about 18 or 19 years). A similar correction is often applied to the solar spheres, the third requiring a 1-year period and the second a long period. (Eudoxus did consider the Sun to have the small motion explained by the third sphere, as Hipparchus reports, quoting the Mirror: "the Sun
differs in where it appears at the solstices." This Eudoxus's planetary theory accounted for
geocentrically reasonable view was held by other most of the easily observed phenomena of all
Greek astronomers, but Hipparchus defined the seven planets and, though modified by Callippus,
center of the zodiac band as the ecliptic circle, on Aristotle, and Autolycus, was not superseded
which the Sun traveled, thus rendering Eudoxus's for almost four generations (by Apollonius).
third solar sphere otiose.)
The qualitative nature of the model colored astro-
Eudoxus took no account, and maybe had no nomical thinking through Ptolemy (who spoke
knowledge, of the longitudinal variation in lunar of planets as carried-on segments of spheres) and
velocity and ignored the annual variation in solar thus through the era of Johannes Kepler.
velocity. (See above.)
When ancient or medieval astronomers wrote of
Each of the other five planets had a total of four the harmony of the spheres, it was to these
spheres, either to explain retrograde motion or the spheres that they referred (though Eudoxus him-
varying intervals of their phases of visibility. The self did not subscribe to the notion).
third sphere's poles lay on the equators of the
second spheres, those of Mercury and Venus coin-
ciding, the others differing. These spheres rotated with synodic periods (the interval between
corresponding position with respect to the Sun), evidently given to an accuracy of 1/3 month. Preserved by Simplicius they are as shown below:
"close to 13 months" "close to 13 months"
378 days 399 days
Aristotle. Metaphysics. 12.8.1073b171074a15. Dicks, D. R. (1970). Early Greek Astronomy to Aristotle. Ithaca, New York: Cornell University Press, pp. 151189. Diogenes Laertius. Lives of Eminent Philosophers. 8.8690.
Mars Mercury Venus
"8 months and 20 days" "110 days" "19 months"
780 days 116 days 584 days
(The third column gives the corresponding modern average periods; the value for Mars is
Evans, James (1998). The History and Practice of Ancient Astronomy. New York: Oxford University Press, pp. 305312. Folkerts, Menso (1998). "Eudoxos ." In Der neue Pauly: Encyclopadie der Antike, edited by Hubert Cancik and Helmuth Schneider. Vol. 4, cols. 223225. Stuttgart: J. B. Metzler.
so discordant that scholars often amend the Greek to "8 months and 20.") The fourth sphere carried the planet (on or near its equator) and rotated with the same period as,
Fowler, David. "Eudoxus: Parapegmata and Proportionality." In Suppes et al., pp. 3348. Geminus (1975). Introduction aux Pheґnome`nes, edited by Germaine Aujac, pp. 98108. Paris: Belle Lettres. (Eudoxus' calendar.)
but oppositely and at an individual small inclination to, the third sphere. Their combined motion produced a figure-eight-shaped curve called by Eudoxus a hippopede^ and carried along the zodiac
Guthrie, W. K. C. (1978). "Eudoxus." In A History of Greek Philosophy. Vol. 5, pp. 447457. The Later Plato and the Academy. Cambridge: Cambridge University Press. Huxley, G. L. (1971). "Eudoxus of Cnidus." In Dictionary
by the motion of the second sphere. There were ancient objections to the theory's predictions of planetary latitude, and Polemarchus noted that it could not explain the
of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 4, pp. 465467. New York: Charles Scribner's Sons. Lasserre, Francёois (1966). Die Fragmente des Eudoxos von Knidos. Berlin: W. de Gruyter. (See critical review
variations in apparent lunar size or in the apparent brightness of Mars and Venus. Giovanni Schiaparelli's reconstruction of Eudoxus's model could not match the observed retrograde
by G. J. Toomer(1968). Gnomon 40: 334337.) Mendell, Henry. "The Trouble with Eudoxus." In Suppes et al., pp. 59138. Neugebauer, Otto (1975). A History of Ancient Mathemat- ical Astronomy. 3 pts. New York: Springer-Verlag,
motion of Venus or Mars (with either period), but our evidence possesses enough gaps to allow various interpretations, some of which generate motions very close to the observed.
pt. 2, pp. 674683. Santillana, Giorgio de (1940). "Eudoxus and Plato: A Study in Chronology." Isis 32: 248262. Simplicius. Commentary on Aristotle, On the Heavens. 2.12.221a.
Suppes, Patrick et al. (eds.) (2000). Ancient and Medieval Traditions in the Exact Sciences. Stanford: Center for the Study of Language and Information. Toomer, G. J. (1996). "Eudoxus of Cnidus." In Oxford Classical Dictionary, edited by Simon Hornblower and Antony Spawforth, pp. 565566. 3rd. ed. Oxford: Oxford University Press. Yavetz, Ido (1998). "On the Homocentric Spheres of Eudoxus." Archive for History of Exact Sciences 52: 221278. Euler, Leonhard Andreas Verdun Astronomical Institute, University of Bern, Bern, Switzerland Born Basle, Switzerland, 15 April 1707 Died Saint Petersburg, Russia, 18 September 1783 Euler, Leonhard. Reproduced by permission of offentliche Kunstammulung Basel (Color portrait by Emmanuel Handmann, 1753)
Leonhard Euler made major contributions to celestial mechanics and spherical astronomy, as well as to mathematics and physics. Leonhard's father, Paulus Euler, was a Protestant minister and married Margaretha Brucker in 1706. The family moved to the village of Riehen, near Basle, where Euler spent his childhood. In 1720 he joined the Department of Arts of the University of Basle, where he received the prima laurea (bachelor) in 1722. One year later Euler received the master's degree in philosophy, which was on comparing the world systems and theories of gravitation of Reneґ Descartes and Isaac Newton. In 1723, he joined the Department of Theology, but devoted most of his time to mathematics. Euler was given the opportunity to attend private lectures by Johann Bernoulli, who recognized Euler's extraordinary potential in mathematics. At the age of 18, Euler began his own investigations on mechanics and mathematics. He left Basel in 1727 to accept an invitation of the newly organized Saint Petersburg Academy of Sciences. There he became professor of physics in 1731 and succeeded Daniel Bernoulli. At the young Russian academy, Euler was surrounded by first-rank scientists, such as Jakob Hermann, Bernoulli, Christian Goldbach, and the astronomer and geographer Joseph Delisle, who introduced him to the current problems in theoretical, observational, and practical astronomy. In 1733 Euler married Katharina Gsell, and in 1734 Johann Albrecht was born, the first of their 13 children. Following an invitation from Frederick the Great of Prussia, Euler moved to Berlin with his family in 1741. He was appointed director of the mathematical class of the academy, and deputy of the academy's president, Pierre de Maupertuis. After Maupertuis's death in 1759, Euler continued presiding over the academy, although without the title of president. During this period, he considerably broadened the scope of his investigations and, competing with Jean d' Alembert, Alexis Clairault, and D. Bernoulli, laid theoretical foundations of mathematical physics and astronomy. Conflicts with King Frederick caused Euler to leave Berlin in 1766, and to return to the Saint
Petersburg Academy, with which he had kept (at least approximately) by such theories: (1) the
regular working contacts. Together with his son theory of the motion of the planets around the
Johann Albrecht, Euler was a member of the Sun, in particular the inequalities in the respec-
commission in charge of the management of the tive motions of Jupiter and Saturn (Great
academy in 1766. Illnesses in 1738 and 1766 had Inequality), (2) the motion of the barycenter of
damaged his eyesight, and by 1771 he was the Earth-Moon system around the Sun, consid-
completely blind. Yet his blindness did not lessen ering gravitational interactions of the planets,
his scientific activity.
(3) the motion of the Moon around the Earth,
Euler was a member of the academies of and (4) the rotation and figure of the Earth (luni-
sciences of Saint Petersburg (1731), Berlin solar precession and nutation). For the latter two
(1746), and Paris (1755), and was a fellow of problems both the Earth and Moon had to be
the Royal Society of London (1746). He died of treated as extended rigid bodies. Euler's best-
a brain hemorrhage.
known discovery is the famous equations
Euler's astronomical works address three describing the rotational motion of rigid bodies,
fields of research: celestial mechanics, spherical which appeared (with respect to an inertial frame
astronomy and astronomical geodesy, and geo- of reference) for the first time in 1752. He fin-
and astrophysics ("cosmical physics"). His main ished the theory of the motion of rigid bodies in
interests, however, were focused on celestial 1765. The "Eulerian equations" with respect to
a body-fixed coordinate system also appeared for
Euler developed the theory of the motions of the first time in 1765. He found special solutions
two bodies in his Mechanica, published in 1736, of these equations, in particular in the absence of
which he considered not only as an introduction external torques (Eulerian free nutation). These
to celestial mechanics, but as the foundation of all studies on rigid bodies obviously stimulated
mechanics as well. The novelty of this book is the Euler in 1759 to develop the theory of the two-
use of analysis rather than geometry to describe and three-body problem applied to rigid bodies.
mathematically the free and constrained motions For Euler, empty space was not an acceptable
of point-like masses in empty space as well as in idea. He postulated instead the existence of an
resisting media. Euler studied the motion of omnipresent, extremely thin and subtle continu-
a particle around a central body when subjected ous "matter," characterized by an extremely high
to a central force (Keplerian motion). An impor- elasticity and an extremely low density. This
tant application concerns the determination of the medium is Euler's ether, and he derived gravity
orbits of planets and comets. Stimulated by the from ethereal pressure. Euler also used this model
appearance of two great comets in 1742 and 1744 to explain secular effects in the motions of the
(C/1742 C1 and C/1743 X1), Euler developed Moon (secular acceleration) and the planets
new methods to determine the (elliptical) orbits (long-time variations of the orbital elements,
of planets and the (parabolic) orbits of comets. e.g., gradual shrinking of orbits) caused by ethe-
Euler wrote several treatises on the mutual real resistance. But this model was not sufficient
perturbations of celestial bodies due to the to explain all inequalities, particularly the motion
inverse-square law of gravitation (perturbation of the Moon's apogee. In this case, Euler
theory), usually assuming the accelerations or questioned the validity of the inverse-square
perturbative forces as given and developing law, and formulated and used (in several of his
their effects on the orbital elements. He tried to treatises) the law of attraction in a more general
solve the general problem of perturbation analyt- way. When Clairault "proved" the correctness of
ically, in particular the general problem of three the inverse-square law in the case of the apsidal
bodies. He found solutions for special cases, motion of the Moon in 1750, this matter was
which he called "restricted three-body-prob- definitely settled.
lems." Euler applied these theories to four main The earliest published astronomical tables
astronomical problems that could be solved incorporating perturbations deduced analytically
from the inverse-square law of gravitation appear to have been Euler's Novae et correctae tabulae ad loca lunae computanda and Tabulae astronomicae solis & lunae, published in 1745 and 1746, respectively. Euler developed the formulae of spherical trigonometry and used them for transformations of celestial coordinates, probably inspired by his own studies on the theory of rotation of celestial bodies. He contributed to the reduction of astronomical observations by developing new methods for the determination and calculation of effects such as precession, nutation, aberrations, parallaxes, and refractions, which must be considered when processing astrometric observations of the positions of celestial bodies. Moreover, Euler was aware of the fact that his solar, lunar, and planetary theories could be modeled with sufficient accuracy only by using observations that were reduced correctly. Some of his papers are therefore devoted to the determination of astronomical constants associated with these effects. Euler developed a new and general processing method for the estimation of the solar parallax by transits of Venus, and determined a value that is very close to the present-day value. Euler wrote several papers on the physical constitution of celestial bodies (mainly on comets) as well as on celestial and terrestrial phenomena related to the Earth's atmosphere or its magnetic field. Most prominent is his theory on the physical cause of comet tails, of the northern lights, and of the zodiacal light, which he tried to explain by one and the same physical process. Euler's memoir published in 1752 may be regarded as one of the first studies on photometric astrophysics. He developed a theory of the intensities of illuminations of celestial bodies for stars, planets, and satellites. Euler then tried to determine the distances and physical constitutions of these bodies from their apparent brilliances, and found that "the material of the Sun has to be totally different from any burnable matter on Earth, and that it must be in such a state of heating as no body on Earth could ever be."
Selected References Aiton, E. J. (1956). "The Contributions of Newton, Bernoulli and Euler to the Theory of the Tides." Annals of Science 11: 206223. Bigourdan, G. "Lettres de Leґonard Euler, en partie ineґdite." Bulletin astronomique 34 (1917): 258319; 35 (1918): 6596. Burchkardt, J. J., E. A. Fellmann, and W. Habicht, (eds.) (1983). Leonhard Euler, 17071783: Beitrage zu Leben und Werk: Gedenkband des Kantons BaselStadt. Basle: Birkhauser Verlag. Calinger, Ronald (1983). "Leonhard Euler: The Swiss Years." Methodology and Science 16, no. 2: 6989. -- (1996). "Leonhard Euler: The First St. Petersburg Years (17271741)." Historia Mathematica 23: 121166. EnestroЁm, G. (1910). Verzeichnis der Schriften Leonhard Eulers. Leipzig: B. G. Teubner,. (This bibliography of Euler's works lists 866 printed publications by Euler and 31 by his eldest son Johann Albrecht, who most probably was assisted by his father. Together Albrecht and Leonhard Euler published over 150 treatises on astronomy.) Euler Committee of the Swiss Academy of Sciences, Swiss National Science Foundation, Academy of Sciences of Russia (eds.). Leonhardi Euleri opera omnia. Series prima (Opera mathematica, 29 in 30 Vols.); Series secunda (Opera mechanica et astronomica, 31 in 32 Vols.); Series tertia (Opera physica et Miscellanea, 12 Vols.); Series quarta A (Commercium epistolicum, 9 Vols.); and Series quarta B (Manuscripta, approx. 7 Vols.). Basle: Birkhauser, 1975. Euler, Karl (1955). Das Geschlecht der Euler-SchoЁlpi: Geschichte einer alten Familie. Giessen: Schmitz. Fellmann, Emil A. (1995). Leonhard Euler. Reinbek bei Hamburg: Rowohlt. Forbes, Eric. G. (1971). The Euler-Mayer Correspondence (17511755): A New Perspective on Eighteenth-Century Advances in the Lunar Theory. New York: American Elsevier. Greenberg, John L. (1995). The Problem of the Earth's Shape from Newton to Clairaut: The Rise of Mathematical Science in Eighteenth-Century Paris and the Fall of "Normal" Science. Cambridge: Cambridge University Press. Hakfoort, Casper (1995). Optics in the Age of Euler: Conceptions of the Nature of Light, 17001795. Cambridge: Cambridge University Press. Nagel F, Verdun A (2005). "Geschickte Leute, die was praestiren koЁnnen...", Gelehrte aus Basel an der St. Petersburger Akademie der Wissenschaften des 18. Jahrhunderts. VortraЁge des Symposiums vom 10. Juli 2003 an der Akademie der Wissenschaften von St. Petersburg waЁhrend der "Schweizer Wochen" anlaЁsslich der Feierlichkeiten "300 Jahre St. Petersburg". Deutsch-russische Beziehungen in Medizin und Naturwissenschaften, Bd. 11. Shaker Verlag, Aachen. ISBN 3-8322-2292-8, ISSN 1615-1321.
Todhunter, I. (1873). A History of the Mathematical
"Schweizer Wochen" anlaЁsslich der Feierlichkeiten
Theories of Attraction and the Figure of the Earth
"300 Jahre St. Petersburg". Deutsch-russische
from the Time of Newton to that of Laplace. (Reprint,
Beziehungen in Medizin und Naturwissenschaften,
New York: Dover, 1962.)
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Truesdell, C. A. (1968). Essays in the History of -- (2005). Die Entstehung moderner wissenschaftlicher
Mechanics. Berlin: Springer-Verlag.
Methoden in Leonhard Eulers BeitraЁgen zur Mechanik
Verdun, A. (1998). Bibliographia Euleriana. Bern: Astro-
und Astronomie [The development of modern scien-
nomical Institute University of Bern. (Catalogue of
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Verdun A (2003). Leonhard Eulers EinfuЁhrung
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Jahrhunderts. VortraЁge des Symposiums vom 10. Juli
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Verdun A (2006). Methods of modern exact sciences in
-- (2003). Leonhard Euler und die alte Sternwarte von St.
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M, KuЁhne A (eds) Astronomy as a model for the
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-- (2004). The determination of the solar parallax from
national Symposium Munich, 1012 (recte 2123)
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. Arch Sci 57
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Andreas KuЁhne. (Algorismus, Heft 59). Rauner
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der Wissenschaften von St. Petersburg in ihrer Verdun A (2010). Entwicklung, Anwendung und
GruЁndungszeit [The Academy of Sciences of Saint
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zur Himmelsmechanik [Development, application,
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und Naturwissenschaften, Bd. 11. Shaker Verlag, -- (2010). "Astronomica" im Briefwechsel zwischen
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Verdun A (2005). Leonhard Eulers Leben und Werk Eine UЁ bersicht [Leonhard Euler's life and work an
in the correspondence between Leonhard Euler and Daniel Bernoulli]. Acta Hist Astron 41:169199.
overview]. In: Nagel F, Verdun A (eds) "Geschickte Verdun A (2011). Die (Wieder-) Entdeckung von Eulers
Leute, die was praestiren koЁnnen...", Gelehrte aus
Mondtafeln [The (re-) discovery of Euler's lunar
Basel an der St. Petersburger Akademie der
tables]. N T M 19:271297.
Wissenschaften des 18. Jahrhunderts. VortraЁge Verdun A (2013). Leonhard Euler's early lunar theo-
des Symposiums vom 10. Juli 2003 an der Akademie
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der Wissenschaften von St. Petersburg waЁhrend der
-- (2013). Leonhard Euler's early lunar theories 17251752. Part 2: developing the methods, 17301744. Arch Hist Exact Sci 67(5):477551. Verdun A (2014). Leonhard Euler's early lunar theories 17251752. Part 3: the breakthrough, 17441752. Arch Hist Exact Sci (in preparation). Waff, Craig B. (1976). "Universal Gravitation and the Motion of the Moon's Apogee: The Establishment and Reception of Newton's Inverse-Square Law, 16871749." Ph.D diss., Johns Hopkins University. Wilson, Curtis (1980). "Perturbations and Solar Tables from Lacaille to Delambre: The Rapprochement of Observation and Theory." Pts. 1 and 2. Archive for History of Exact Sciences 22: 53188, 189304. -- (1985). "The Great Inequality of Jupiter and Saturn: From Kepler to Laplace." Archive for History of Exact Sciences 33: 15290. -- (1987). "D'Alembert versus Euler on the Precession of the Equinoxes and the Mechanics of Rigid Bodies." Archive for History of Exact Sciences 37: 233273. -- (1990). "Daniel Bernoulli and Boscovic versus Euler on Planetary Perturbations: 17481752." Bulletin of the American Astronomical Society 22: 1039. (Paper abstract). -- (1992). "Euler on Action-at-a-Distance and Fundamental Equations in Continuum Mechanics." In The Investigation of Difficult Things: Essays on Newton and the History of the Exact Sciences in Honour of D. T. Whiteside, edited by P. M. Harman and Alan E. Shapiro, pp. 399420. Cambridge: Cambridge University Press. -- (1995). "The Problem of Perturbation Analytically Treated: Euler, Clairaut, d'Alembert." In Planetary Astronomy from the Renaissance to the Rise of Astrophysics, Part B: The Eighteenth and Nineteenth Centuries, edited by Reneґ Taton and Curtis Wilson, pp. 89107. Vol. 2B of The General History of Astronomy. Cambridge: Cambridge University Press. Eutocius Thomas Hockey Department of Earth Science, University of Northern Iowa, Cedar Falls, IA, USA Flourished (Israel), circa 500 Eutocius is cited as the author of an introduction to the Almagest. But most scholars doubt that this work ever existed.
Selected Reference Lindsay, Jack (1971). Origins of Astrology. New York: Barnes and Noble. Evans, David Stanley Ian S. Glass South African Astronomical Observatory, South Africa Born Cardiff, Wales, 28 January 1916 Died Austin, Texas, USA, 14 November 2004 In a career that took him to three continents, David Evans made his mark in several fields of observational astronomy including photographic and spectrographic studies of planetary nebulae and galaxies, stellar photometry, spectroscopy, and high-speed photometric studies of transient astronomical events. His later career included valuable historical studies. Evans attended the Cardiff High School for Boys until 1932, and then entered King's College, Cambridge, in 1934 as a major scholar. In 1938 he transferred to Oxford University where, under the direction of Arthur Eddington and Richard van der Riet Woolley, he obtained his Ph.D. in astrophysics in 1941 with a dissertation on the formation of the hydrogen Balmer line spectrum in stellar atmospheres. During World War II, Evans worked as a medical physicist. From 1941 to 1946 he also served on the editorial board
of The Observatory. In October 1945 Evans was appointed second assistant at the Radcliffe Observatory, Pretoria, South Africa, arriving there in early 1946. Working only with untrained laborers, he modified the mirror cell and installed the primary mirror of the 74-in. telescope in 1948. The mirror had arrived 10 years after the mechanical parts and was thinner than anticipated. Since the Newtonian configuration was the only one available at first, Evans undertook a program of photographic astronomy and photometry of southern galaxies and
Evans, David Stanley
planetary nebulae. The pioneering Cape Photo- studies, and the application of a star spot model
graphic Atlas of Southern Galaxies was one to certain variable M-dwarfs.
result of this work. When spectroscopic equip- The cosmic distance scale is based on knowl-
ment designed by Evans for especially high pho- edge of the luminosities of Cepheid variables.
tographic speed became available, Evans One way of obtaining the luminosities involves
obtained the first redshifts measured for brighter determining their radii. From Evans's work on
southern galaxies with the partial collaboration of stellar diameters, and that of Thomas G. Barnes
on near-IR photometry, it was found in 1976
Early in 1951 Evans joined the Royal Obser- that a simple relationship exists between the
vatory, Cape of Good Hope, as chief assistant and surface brightness of a star and its color in
was in charge of the Cape share, amounting to the V-R color index. The Barnes-Evans relation-
one-third of the observing time on the 74-in. ship can be used to determine the radii and
telescope, following an agreement between the distances of pulsating stars by means of light,
British Admiralty and the Radcliffe Trustees. color, and radial velocity measurements during
This observing time was devoted to spectral the pulsation cycle. This technique is an evolu-
classification and radial velocity studies of tionary development of the Baade-Wesselink
stars whose parallaxes had been measured at method.
While residing in South Africa, Evans took an
During the early 1950s, Evans and others rec- interest in the history of astronomy that continued
ognized that a unique series of lunar occultations uninterruptedly since that time. His interest
of Antares and Aldebaran, events that occur on in John Herschel sparked his first historical
a 19-year cycle, would provide an opportunity to project on Herschel's experiences at the
attempt measurements of the angular diameters Cape. Since then, Evans wrote a biography of
of these stars. Using conventional photometric the Abbeґ Nicolas de Lacaille, another astro-
techniques, five successful observations were nomical visitor to the Cape, and then a general
obtained of the occultation of Antares. Evans history of astronomy in the Southern Hemisphere
analyzed the data from these occultations and (Under Capricorn). Later he collaborated in a
concluded that Antares was possibly history of the McDonald Observatory after arriv-
nonspherical or severely spotted. Although ing in Texas. He also edited several volumes of
Evans's results were met with skepticism at the symposium proceedings. At Oxford University,
time, his analysis has been vindicated by interfer- he was for several years scientific editor of the
ometric measurements as well as by later occul- journal Discovery now merged with the New
Evans was instrumental in the selection of the In September 1984 Evans was named as the
Sutherland site for what became the South first Jack S. Josey Centennial Professor in Astron-
African Astronomical Observatory.
omy by his colleagues and the University of
Evans spent the academic year 1965/1966 as Texas Board of Regents. A symposium was held
a senior visiting scientist fellow at the University in Evans's honor at the University of Texas on
of Texas. On 4 October 1968 he resigned from the 1819 September 1986, when he became emeri-
Royal Observatory, where he had reached the tus professor.
civil service rank of senior principal scientific Evans received the Tyson Medal (1937) and
officer, to become a professor of astronomy and a Rayleigh Prize (1938) from Cambridge Univer-
associate director for research at the University of sity, and the Macintyre Award for Astronomical
Texas at Austin and at the McDonald Observa- History (1972) and the Gill Medal (1988), both
tory. His research included further development from the Astronomical Society of Southern
of the high-speed photometric occultation tech- Africa. On retirement, he and his wife were
nique for determining stellar diameters, the use of made honorary citizens of Texas by the state's
precise time-resolution techniques in flare star Governor.
Evans, John Wainwright
On 8 March 1949 Evans married Betty Hall Hart. They have two children, Jonathan Gareth Weston Evans and Barnaby Huw Weston Evans. Selected References Barnes, Thomas G. and David S. Evans (1976). "Stellar Angular Diameters and Visual Surface Brightness I: Late Spectral Types." Monthly Notices of the Royal Astronomical Society 174: 489512. Barnes III, Thomas G. (ed.) (1987). "The Jack S. Josey Centennial Professorship Symposium in Honor of David S. Evans." Vistas in Astronomy 30: 196. Evans, David S. (1946). Frontiers of Astronomy. London: Sigma. -- (1952). Teach Yourself Astronomy. London: English Universities Press. -- (1988). Under Capricorn: A History of Southern Hemisphere Astronomy. Bristol: A. Hilger. -- (1998). The Eddington Enigma: A Personal Memoir. Princeton, New Jersey: D. S. Evans. -- (1992). Lacaille: Astronomer, Traveler. Tucson, Arizona: Pachart. Evans, David S., B. H. Evans, Terry Deeming, and S. Goldfarb (1969). Herschel at the Cape. Austin: University of Texas Press. Evans, David S. and J. D. Mulholland (1986). Big and Bright: A History of the McDonald Observatory. Austin: University of Texas Press. Evans, John Wainwright J. McKim Malville Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO, USA Born New York, New York, USA, 14 May 1909 Died Santa Fe, New Mexico, USA, 31 October 1999 John Wainwright Evans was born in New York City on 14 May 1909. He died at home in Santa Fe, New Mexico, on 31 October 1999. He received a Bachelor's degree in mathematics from Swarthmore College in 1932. From Harvard he received a Master's degree in astronomy in 1936 and a Doctorate in astronomy in 1938.
Bart Bok was his PhD thesis advisor. He was first director of the Sacramento Peak Observatory, which he built into a world-class solar observatory. From 1938 to 1942 he was an instructor and assistant professor of mathematics and astronomy at Mills College, Oakland, California, where he also worked at the Chabot Observatory. It was at this time that he independently invented the birefringent filter, which had already been invented by Bernard Lyot and Yngve Ohman. Evans worked at the Institute of Optics of the University of Rochester from 1942 to 1946, where he developed a number of optical devices for military use. In 1946 he was hired by the High Altitude Observatory, working under Walter Orr Roberts until 1952, when he left to become director of Sacramento Peak Observatory. On 4 June 1946, 4 months after joining the staff of HAO, he was operating the Climax coronagraph by himself and spotted the "great granddaddy" of solar prominences in the eyepiece. He found he could not fit a prominence into the picture frame and rushed to ask Roberts for advice. Roberts replied that there never has been a prominence that large and that he must be doing something wrong. When Roberts came over to the observatory to check out the telescope, he reported that he nearly fainted at the size of the eruptive prominence, which appeared to be a huge magnetic torus gradually unwinding as it rose above the sun. That prominence became one of the signature observations of the Climax observatory. While at the High Altitude Observatory, Evans developed a split-element birefringent filter, which is more transparent and has a wider field of view than the initial design. He developed an externally occulted coronagraph, which has been used on satellites such as the white-light coronagraphs on Skylab and Solar Maximum Mission. He also developed what is now known as the Evans sky photometer, which has been used to monitor sky brightness in site surveys around the world. Soon after the end of the Second World War, Donald Menzel proposed that a second coronagraph station should be established in New
Evans, John Wainwright
Mexico as a supplement to the Climax corona- the theory of narrow-band, tunable optical filters
graph. As early as 1947 the shortcomings of the in his derivation of an exact analytic expression Climax site were becoming evident. There were for the spectral transmittance of S olc-type filters,
too many cloudy days on the Continental Divide, which previously could be analyzed only by labo-
increasingly due to jet condensation trails and rious numerical methods. He then applied the activity at the adjacent Climax mine occasionally S olc filter to a tunable monochromator, permit-
reduced the clarity of the atmosphere. In 1947 ting the use of high-order gratings. He designed
Evans sky photometers were used for site testing a double-pass spectrograph for reduction of
at Sacramento Peak, which had been chosen as instrumentally scattered light in solar absorption
a possible site because of its proximity to White lines, which he incorporated into his design of the
Sands testing grounds, near Alamogordo. The Air Sac Peak spectroheliograph which is still used in
Force was particularly interested in establishing daily monitoring of solar activity. He pioneered
an observing station on the summit of Sacra- the idea of using a sun-pointed solar spar on
mento Peak to track V2 rockets fired from which multiple separate solar telescopes could
White Sands. In 1949 observations at be mounted, with a roller-type drive to give
Sacramento Peak commenced with open-air high precision and smooth guiding. He designed
telescopes run by Harry Ramsey and George the solar flare patrol telescope, which became
Schnable. In 1952 a 26 ft spar was installed inside the standard for the International Geophysical
the new dome at Sacramento Peak, and Evans Year. Evans also designed a DopplerZeeman
became director. He continued in that capacity Analyser for measuring solar magnetic fields
until 1972 gathering an outstanding scientific with high linearity as well as one of the first
staff and building one of the world's leading vector magnetographs.
solar observatories. Menzel had originally Evans led two eclipse expeditions to observe
hoped there would also be a radio observatory at the height-resolved chromospheric spectrum to
Sacramento Peak, but the extensive telemetry Khartoum in 1952 and to Puka-Puka in the South
facilities at White Sands rendered it unsuitable. Pacific in 1958. For these he designed a slitless
A solar radio observatory was established at Fort spectrograph and a jumping-film camera. Unfor-
Davis, Texas, by Alan Maxwell in 1956, which tunately, Evans had a terrible accident a few days
became Menzel's third western observatory, after before the Khartoum eclipse. He fell off the tele-
Climax and Sacramento Peak. Although Menzel scope, which somebody forgot to tie down, and it
had hoped that these observatories would become started to swing. He jumped off and hit the con-
part of an extensive program of solar physics at crete pier, fracturing his ankle. Two of HAO staff,
the Harvard College Observatory, Harvard was Robert Lee and Robert Cooper, succeeded in mak-
unwilling to provide tenured positions for Sacra- ing the necessary optical alignments, guided by
mento Peak astronomers. The Air Force stepped Evans lying nearby on a litter. The data from the
in and the observatory became the Air Force's Khartoum eclipse were critical in establishing the
new Upper Air Research Observatory.
High Altitude Observatory as a major research
Evans served on the Editorial Board of Solar institution in solar physics. In the hands of Richard
Physics from its inception in 1967 to 1976.
Thomas and Grant Athay, the results of the Khar-
His research was characterized by constant toum expedition firmly established the nature of
innovations in the field of optics. His invention non local thermodynamic equilibrium (non-LTE)
of the split-element version of the Lyot filter in the chromosphere.
represented a major advance in the design of In 1958 he obtained data during the progress
this type of optical filter. In 1949 he developed of a flare that showed, for the first time, associ-
the design of the polarizing two-beam- ated changes in sunspot magnetic fields. In 1960,
interferometer form of Lyot filter that today is he initiated studies of small-scale motions in the
the basis of many helioseismic imaging pro- solar atmosphere, obtaining the first quantitative
grams. He made a further major contribution to measurements of the velocity amplitudes as
functions of line strength and height in the solar atmosphere. Evans was the third recipient (1982) of the Hale Prize of the Solar Physics Division of the American Astronomical Society. He won the David Richardson Medal (1987) of the Optical Society of America and was given Honorary Doctor of Science degrees by the University of New Mexico (1967) and Swarthmore College (1970). He received the Newcomb Cleveland Prize of the American Association for the Advancement of Science (1957) and was elected a Fellow of the American Academy of Arts and Sciences (1964). He received a number of prizes and awards from the Air Force such as the Rockefeller Award for Distinguished Public Service (1969), the Distinguished Civilian Service Award (1965), the Guenter Loeser Memorial Award (1967), and the Outstanding Achievement Award (1970). References Bogdan, Thomas J. (2002). Donald Menzel and the Beginnings of the High Altitude Observatory. Journal for the History of Astronomy Xxxiii: 157192. Dunn, Richard B., George W. Simon, Raymond Smartt, and Jack B. Zirker. (2000a). Jack Evans obituary. Solar Physics 191: 227229. Dunn, Richard B., et al. (2000b). John Wainwright Evans, 19091999. Bulletin of the American Astronomical Society 32: 16631665. --. (2000). "Evans John W." Solar Physics 191: 227229. Evans, John W. (1940). The Quartz Polarizing Monochro- mator. Publications of the Astronomical Society of the Pacific 52: 305311. Evans, John W. (1958). Solc Birefringent Filter. Journal of the Optical Society of America 48: 142143. Evans, John W. (1964). Inclined Inhomogeneities in the Solar Atmosphere. Astrophysica Norvegia 9: 3344. Evans, John W. (1967). Sacramento Peak Observatory. Solar Physics 1: 157161. Evans, John W. (1968). Color in Solar Granulation. Solar Physics 3: 344345. Liebowitz, Ruth Prelowski. (2002). Donald Menzel and the Creation of the Sacramento Peak Observatory. Journal for the History of Astronomy xxxiii: 193211. Roberts, Walter Orr. (1983). Interview with Dr. Walter Roberts by David DeVorkin. Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA. http://www.aip.org/history/ohilist/ 28418_1.html Zirker, J.B. (1984). Total Eclipses of the Sun. New York: Van Nostrand Reinhold
Evershed, John Keith Snedegar Utah Valley State College, Orem, UT, USA Born Gomshall, Surrey, England, 26 February 1864 Died Ewhurst, Surrey, England, 17 November 1956 English solar astronomer John Evershed is remembered largely for the discovery of the effect that bears his name, the radial outflow of gas in sunspots at a speed not much more than 1 km sА1. Evershed was the seventh child of John and Sophia (neґe Price) Evershed. He was educated at schools in Brighton and Croydon. Toward the end of his life Evershed recalled his scientific curiosity first being aroused by a partial solar eclipse. At age 13 he built a small telescope to observe Mars during its favorable 1877 opposition. His brother Sydney introduced him to professional scientific circles, and as a young man he met Charles Darwin and Alfred Wallace. Evershed developed an interest in lepidoptera and other insects, but studying the Sun was to be his lifelong passion. The friendship of Arthur Ranyard proved especially influential in this regard. Ranyard introduced Evershed to George Hale, and he bequeathed Evershed his 18-in. reflecting telescope. Between 1890 and 1905 Evershed made a long series of observations of solar prominences from his private observatory at Kenly. During this period a manufacturing firm employed him in the analysis of oils and other industrial substances. The company granted Evershed leave to join the British Astronomical Association solar eclipse expeditions to Norway in 1896 and India in 1898. The 1896 eclipse was clouded out, but on the expedition Evershed met his future wife, Mary Acworth Orr ( Mary Evershed). The 1898 eclipse was more of a scientific success. At the beginning and at the end of the eclipse, Evershed observed the "flash" spectrum of emission from gas that would normally be a source of
absorption features when light from the solar rotation. Evershed finally closed his observatory
photosphere passes out through it, and showed in 1953, when he was 89 years old.
that the spectral features had essentially the same Evershed was a founding member of the
pattern in emission as in absorption. In addition, British Astronomical Association. He served as
he obtained the first photograph showing that the director of the solar spectroscopy section in
continuous (reflected) light from the corona 18931899 and director of the spectroscopy
extended blueward of the Balmer limit at section in 19241926. In 1915 Evershed was 3,646 A° . For the 1900 eclipse in Algeria, elected a fellow of the Royal Society; 3 years
Evershed chose a site near the southern limit of later he received the Gold Medal of the Royal
totality, because from this vantage point the dura- Astronomical Society. Upon his retirement from
tion of the "flash" was increased. Although his Kodaikanal, Evershed was made a Companion of
site was actually south of the limit, he again the Indian Empire.
obtained valuable data.
Evershed was an instrument maker at heart.
The eclipse results were published by the All of his eclipse equipment was homemade. He
Royal Society and led to an acquaintance with also designed a spectroheliograph independent of
Sir William Huggins. It was through the rec- Hale's invention of the instrument. At
ommendation of Huggins that the India Office Kodaikanal, Evershed built a high-dispersion
appointed Evershed assistant to C. Michie Smith spectrograph and a spectroheliograph for photog-
at the Kodaikanal Observatory in 1906. In 1911 raphy in hydrogen light. At Ewhurst he
he succeeded Smith as the director of the obser- experimented with large hollow prisms filled
vatory. Much of his work at Kodaikanal was on with ethyl cinnamate to increase the resolution
the spectrum of sunspots. In 1909 Evershed first of spectrograms.
measured the Doppler shifts of umbral and pen- In 1906 Evershed married Mary Orr. She was
umbral gases moving radially outward from a loving companion and an active collaborator of
a sunspot. The phenomenon came to be known his observational programs, as well as the author
as the Evershed effect. In addition to his solar of Dante and the Early Astronomers and Who's
work, Evershed obtained spectra of Halley's Who in the Moon. She died in 1949. In 1950
comet (IP/Halley), Nova Aquilae 1918, and Evershed married Margaret Randall. There were
dark clouds in the Milky Way. Also during his no children.
stay in India, Evershed set up a temporary
observing station in Kashmir (where he found
exceptionally good observing conditions) and served as an advisor on the establishment of an
observatory in New Zealand. It was from Kashmir that Evershed obtained a 1915 spectrogram of the Sun that he concluded might marginally show the predicted Einsteinian gravitational redshift of solar absorption lines. The expected shift is rather less than either the Evershed flow or the convective velocities in the solar atmo-
Evershed, John (1901). "Solar Eclipse of May 28, 1900. Preliminary Report of the Expedition to the South Limit of Totality to Obtain Photographs of the Flash Spectrum in High Solar Latitudes." Proceedings of the Royal Society of London 67: 370385. -- (1901). "Wave-length Determinations and General Results obtained from a Detailed Examination of Spectra Photographed at the Solar Eclipse of January
sphere, and what he observed was clearly a mix of the three effects, which have only rather recently been sorted out. He retired from Kodaikanal in 1923, returned to England, and established a private observatory at Ewhurst. Work carried out during these later years included consultation with Hale on the Sun's magnetic field, and continuing studies of solar
22, 1898." Philosophical Transactions of the Royal Society of London A 197: 381413. -- (1909). "Radial motion in Sunspots." Kodaikanal Observatory Bulletin 18. -- (1911). "The Auto-Collimating Spectroheliograph of the Kodaikanal Observatory." Monthly Notices of the Royal Astronomical Society 71: 719723. -- (1919). "The Spectrum of Nova Aquilae." Monthly Notices of the Royal Astronomical Society 79: 468490.
Evershed, Mary Ackworth Orr
-- (1927). "The Solar Rotation and the Einstein Displacement Derived from Measures of the H and K Lines in Prominences." Monthly Notices of the Royal Astronomical Society 88: 126134. -- (1936). "Notes on a Liquid-Prism Spectrograph: Addendum." Observatory 59: 309310. -- (1955). "Recollections of Seventy Years of Scientific Work." Vistas in Astronomy 1: 3340. Laurie, P. S. (1971). "Evershed, John." In Dictionary of Scientific Biography, edited by Charles Couliston Gillispie. Vol. 4, pp. 497498. New York: Charles Scribner's Sons. Stratton, F. J. M. (1957). "John Evershed." Biographical Memoirs of Fellows of the Royal Society 3: 4151. Evershed, Mary Ackworth Orr Mary T. Bruck University of Edinburgh, Edinburgh, Scotland Born Plymouth Hoe, Devon, England, 1 January 1867 Died Ewhurst, Surrey, England, 25 October 1949 British solar physicist, historian of astronomy, and Dante Alighieri scholar Mary Evershed made important contributions to observations of solar prominences and their classification, with some, but not all, of the work done in collaboration with her husband John Evershed. The work resulting in the discovery of what is now called the Evershed effect (horizontal flow of gas in the penumbrae of sunspots) was done by John Evershed early in their marriage. She was born Mary Acworth Orr, a daughter of Andrew Orr, an army officer (who died when Mary was only 3 years old), and his wife Ruth. After the father's death, the children were brought up by their mother in the home of their clergyman grandfather, in a vicarage near Bath. Mary and her sister Lucy received their education entirely at home from an enlightened governess who, when Mary was 20, took the sisters abroad to study languages and the arts in Germany and Italy. They spent the Mary T. Bruck: deceased.
years 18881890 in Florence where Mary became fascinated by the work of the poet Dante Alighieri and particularly by the astronomical references that abound in his Divine Comedy. After this period of study, the family moved to Australia, living near Sydney for 5 years. During this time Mary developed her knowledge of astronomy, encouraged by John Tebbutt, the well-known amateur astronomer and comet discoverer who was Australia's leader in the field at the time. The result was An Easy Guide to the Southern Stars (1897; second edition: 1911), a small atlas intended for beginners containing maps of recognizable naked-eye stars and star groups visible from the latitude of Australia. On returning to Britain, Mary became an active member of the recently founded British Astronomical Association. She settled in Frimley, Surrey, and acquired a 3-in. (7.6-cm) refractor with which to make serious observations of double and variable stars. She also took part in the association's eclipse expeditions to Finnmark and Algiers. On the first of these, in 1896, she met John Evershed whom she would marry. John Evershed, an amateur astronomer who specialized in solar spectroscopy and had built a number of excellent spectroscopes, had in 1892 constructed a spectroheliograph according to the design of its inventor, George Hale. John was soon recognized as one of the leading practitioners of solar spectroscopy. In 1906 he was offered a professional appointment as assistant astronomer at the Observatory at Kodaikanal in India. In that year he and Mary were married and traveled to India by way of the United States and Japan. John took up his appointment in 1907 and in 1911 was made director of the observatory when that post fell vacant. The Eversheds remained in India until his retirement in 1923. The Eversheds had no children, but Mary's nephew, Andrew Thackeray, stimulated by their example, became an astronomer and director of the Radcliffe Observatory in Pretoria, South Africa. Though not an official member of staff, Mary gave valuable assistance to her husband on various astronomical missions, including sitetesting expeditions to Kashmir and New Zealand
and an eclipse expedition to Australia in 1922 The Eversheds retired to England in 1923.
(which was, however, frustrated by the weather). Mary now devoted her energies to the British
In the observatory, she made herself familiar with Astronomical Association. She founded and
spectroheliograph work, her special interest became head of the association's historical
being solar prominences. In 1913 she published section, contributing numerous charming articles
a substantial paper in the Monthly Notices of the to its Journal.
Royal Astronomical Society (read in person at The most ambitious of Mary's historical
a meeting of the society when the Eversheds projects was the compendium Who's Who in the
were in London on leave) in which she analyzed Moon, edited by her, a directory identifying every
records of prominences associated with sunspots person named in the lunar formations. For this
made between 1908 and 1910. She was able to task she enlisted the help of a team of astrono-
classify these as active and eruptive and to track mers from Britain and abroad. This fascinating
their motions from photographs taken at brief directory is currently (2002) being revised.
intervals, thus anticipating cinematography with Mary Evershed died of cancer at her home in
the coronagraph later. Mary pursued the same Surrey.
research in a joint paper with her husband,
published in 1917 by the Kodaikanal Observa-
tory. The analysis was principally hers and Selected References
involved almost 60,000 individual prominence observations covering an entire sunspot cycle. During her years at Kodaikanal, which she found an ideal place to write on astronomy and poetry, Mary also pursued her studies of Dante Alighieri, which culminated in her book, Dante and the Early Astronomers (1914), published under the name, "M. A. Orr (Mrs. John Evershed)." There she demonstrated the poet's considerable knowledge of the astronomy and cosmology of his day and elucidated the astronomical allusions in the Divine Comedy that he used to indicate date, hour, or passage of time. These references are largely obscure and require knowledge of astronomy as well as classical and historical sources. The Divine Comedy is an account of the poet's imaginary journey
Bruck, Mary T. (1998). "Mary Acworth Evershed neґe Orr (18671949), Solar Physicist and Dante Scholar." Journal of Astronomical History and Heritage 1: 4559. Evershed, J. E and M. A. Evershed (1917). "Results of Prominence Observations." Memoirs of Kodaikanal Observatory 1. Evershed, M. A. (1913). "Some Types of Prominences associated with Sun-spots." Monthly Notices of the Royal Astronomical Society 73: 422430. -- (ed.) (1938). Who's Who in the Moon. Memoirs of the British Astronomical Association. Vol. 34, pt. 1. Edinburgh. Orr, M. A. (1897). An Easy Guide to the Southern Stars. London: Gall and Inglis. (2nd ed. 1911.) -- (1914). Dante and the Early Astronomers. London: Gall and Inglis. -- (1956). Dante and the Early Astronomers, Revised by B. Reynolds. London: Allan Wingate. Reynolds, Barbara (1950). "Obituary Notice and
through Hell, Purgatory, and Heaven, which takes place over a fixed period of time. Mary's account of this journey, based on its scientific references, was described by Dorothy Sayers, a well-known
Retrospective Review." Italian Studies 5: 7275. Thackeray, A. D. (1950). "Mary Ackworth Evershed." Monthly Notices of the Royal Astronomical Society 110: 128129.
translator of the poem, as "quite the best guide
available to Ptolemaic astronomy and to Dante's
handling of celestial phenomena." A second edi- tion of the book, revised by the Dante Alighieri Ezra
scholar Barbara Reynolds, appeared in 1956, some
years after the author's death.
Ibn Ezra: Abraham Ibn Ezra