Astronomers
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Adams, John Couch (1819-1892),
English astronomer and mathematician, was born at Laneast, Cornwall, June
5, 1819. He attended St. Johns College, Cambridge. Adams' solution to the
inverse perturbation problem led him, on the basis of unexplained irregularities
in the motion of the planet Uranus, to suggest (1845) the existence of
a more distant undiscovered planet -- a conclusion also reached by Urbain
Jean Joseph Leverrier a year later and confirmed in 1846 by the discovery
of Neptune near their predicted positions. Adams was appointed the Lowndean
professor of astronomy and geometry at Cambridge in 1859 and director of
the Cambridge Observatory in 1861. He later worked on the secular acceleration
of the moon's mean motion and analyzed the perturbations of the Leonid
meteors. He died at Cambridge, Jan. 21, 1892
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Barnard, Edward Emerson (1857-1923),
American astronomer, the discoverer of Barnard's Star and the first to
sight Jupiter's fifth satellite in 1892. He is best known for his book
of photographs, Atlas of Selected Regions of the Milky Way , and for his
identification of sixteen comets.
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Bode, Johann Elert (1747-1826),
German astronomer, popularized an empirical law, later named after him,
which gives the approximate distances of the planets from the sun. He also
named the planet Uranus, ending the confusion caused by William Herschel's
desire to name it Georgium Sidus after King George III of England.
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Brahe, Tycho (1546-1601), Danish
astronomer born at Knudstrup Manor, then in Denmark, now Sweden, Dec. 14,
1546. He studied at the universities of Copenhagen and Leipzig, and became
interested in science. He found that astronomical tables based on the Ptolemaic
system were highly erroneous. Soon Tycho began practical observations with
crude instruments. In 1572 he observed the appearance of a supernova, since
called Tycho's Star. Discovery of this star was a blow to the old
school, which believed in the immutability of stars. On the island of Hveen,
Tycho established an elaborate observatory and labored for many years.
His work on practical astronomy of the sun, moon, comets, and planets was
the finest accomplished in pretelescope times. Tycho abandoned the Ptolemaic
theory but did not accept the Copernican; he took a halfway position, the
result being the "Tychonic system." Tycho's theory was that the earth was
stationary, with the moon and sun circling it, but the other planets revolved
around the sun. In 1600 he moved to Prague and came to know Johannes Kepler.
His most important accomplishment was the great series of planetary observations
which he left with Kepler. Tycho died at Prague, Oct. 24, 1601. See also
Astronomy: Astronomical Instruments; Kepler, Johannes
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Brown, Ernest William (1866-1938),
American astronomer whose book, Tables of the Moon , is the leading work
on the moon's complex motion. Brown showed the existence of changes in
the earth's rotation, and extended his research to planetary theory, asteroids,
resonance, and the three-body problem.
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Campbell, William Wallace (1862-1938),
American astronomer, pioneered in the determination of radial velocities
of stars. He determined the sun's motion in the galaxy as well as the average
random velocity of thousands of stars of various spectral types. He was
credited by Albert Einstein as a contributor to the proof of the theory
of relativity.
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Cannon, Annie Jump (1863-1941),
American astronomer, specialized in the determination of stellar spectra.
She classified the spectra of more than 400,000 stars in compiling the
Henry Draper Catalogue and the Henry Draper Extension . Miss Cannon
also discovered five novas and more than 300 variable stars.
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Cassini, Giovanno Domenico (1625-1712),
Italian-French astronomer and engineer, was born in Italy but became a
French citizen in 1673, changing his name to Jean Dominique Cassini. He
discovered four satellites of Saturn and the concentric division, which
now bears his name, of that planet's ring; studied and named the zodiacal
light; measured the rotational periods of Mars, Venus, and Jupiter; and
showed the cause of the moon's libration. He served as the director of
the Paris Observatory, a post to which he was succeeded in turn by his
son, Jacques Cassini (1677-1756), his grandson, César François
Cassini de Thury (1714-1784), and his great-grandson, Comte Jacques Dominique
de Cassini (1747-1845).
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Challis, James (1803-1882),
English astronomer who sighted, but failed to report, the planet Neptune
on two occasions in 1846, more than a month before it was first reported
from Berlin. He is also the author of a twelve-volume work, Astronomical
Observations Made at the Observatory of Cambridge (1832-1864).
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Copernicus, Nicolaus (Pol.
Mikolaj Kopernik; Ger. Niklas Koppernigk) (1473-1543), Polish astronomer,
often regarded as the founder of modern astronomy.
Life
Copernicus was born on Feb. 19, 1473, at
Torun (Thorn) on the Vistula, the youngest of four children of Mikolaj
Kopernik, a merchant and magistrate, and of his wife, Barbara Waczenrode
(or Watzenrode). Upon the death of his father in 1483, Copernicus was adopted
by his maternal uncle, Lucas Waczenrode, a priest, who destined him for
a career in the church. After schooling at Torun, Copernicus (who early
adopted this Latinized name) went to the University of Cracow and in 1496
to Italy, where he studied canon law at the universities of Bologna and
Padua, receiving his doctorate at Ferrara. At Padua he underwent a course
of medical training and then spent a year in Rome. By 1506 Copernicus had
returned from Italy to live at Heilsberg as physician to his uncle, who
had become bishop of the Prussian diocese of Ermland (or Warmia) and who
had secured his nephew's appointment as a canon in the diocesan cathedral
of Frauenburg. Copernicus spent the rest of his life at Frauenburg except
when administrative or political duties required his presence elsewhere.
He assumed special responsibilities on behalf of the chapter during the
hostilities of 1519 between Poland and the Teutonic Knights. In 1522 his
proposals for remedying the postwar debasement of the coinage were presented
before the Diet of Graudenz. He also exercised his medical skill on his
fellow ecclesiastics and (according to tradition) on the poor. However,
the most significant achievement of his mature years was his laborious
composition of the historic book that was to herald the overthrow of the
medieval conception of the universe.
As a student at Cracow, Copernicus had already
begun to apply his mind to the classic problem of tracing mathematical
order in the complicated motions of the heavenly bodies. The solution of
this problem generally accepted in his day, which had been formulated by
Ptolemy of Alexandria in the second century a.d., was that the central
position in the universe was assigned to the earth, around which the sun,
moon, and planets revolved. While in Italy, Copernicus was influenced by
a revival of early Greek scientific ideals which aimed at representing
the planetary motions with the greatest attainable mathematical simplicity.
These ideals had already inspired Aristarchus of Samos (third century b.c.),
the unheeded "Copernicus of Antiquity," to suggest placing the sun instead
of the earth at the center of the universe. It was this heliocentric (or
sun-centered) arrangement of the planets that Copernicus sought to introduce
and which was eventually adopted when conservative opposition had been
overcome (see Fig. 1).
About 1512 Copernicus circulated among his
friends a manuscript Commentariolus, giving a short preliminary account
of his system. Following his settlement at Frauenburg he observed the heavens
from a platform on the wall enclosing the precincts of the cathedral. He
employed home-made instruments constructed according to Ptolemy's prescriptions.
By combining his observations with others recorded by his predecessors
(and somewhat uncritically accepted by Copernicus), he was able to determine
the various constants by which the planetary orbits were to be defined.
In 1539 Copernicus was visited by the Wittenberg mathematician Georg Joachim
von Lauchen, called Rheticus, who came to Frauenburg to acquaint himself
with the details of the rumored reformation of astronomy and to examine
the manuscript of the great book, now nearing completion. In the following
year Rheticus published a summary of the earlier chapters under the title
De libris revolutionum narratio prima. When at last Copernicus had been
persuaded to authorize the publication of the entire work, Rheticus arranged
for it to be printed at Nuremburg in 1543 under the title De revolutionibus
orbium coelestium libri VI. While the De revolutionibus was still on the
press Copernicus became ill, and he died at Frauenburg on May 24, 1543,
just after receiving the first copy of his book.
Character
The interests of Copernicus were wide and
his accomplishments were not confined to astronomy. Mention has already
been made of his medical practice and of his studies on the coinage. He
was also a diplomat, a mathematician, a linguist, and an artist: a copy
of his self-portrait survives. One of the few Greek scholars of his day
in northeastern Europe, he published in 1509 a Latin translation of the
Greek Epistles of the seventh-century Byzantine poet Theophylactus Simocatta.
His position in the Reformation controversy appears to have been that of
a Catholic "moderate" anxious to avoid a split in the church. The
resolute tenacity of his character is attested by his success in achieving
his lifelong purpose in the face of learned opposition and ignorant prejudice.
Copernicus dedicated his book to the reigning
pope, Paul III, whose protection he claimed for his speculations and to
whom he commended his solar and lunar tables as a contribution to the problem
of reforming the calendar, which had recently been under discussion by
the fifth Lateran Council. These tables, indeed, helped toward the reform
carried out in 1582 by Pope Gregory XIII.
The Copernican Theory
Of the six books into which the De revolutionibus
is divided, the first sets forth the essential Copernican doctrines that
the daily rising and setting of the heavenly bodies is a consequence of
the daily rotation of the earth on its polar axis; and that the apparent
travel of the sun through the zodiacal constellations, and the phenomena
of the seasons, can be attributed to an annual revolution of the earth
about the sun in a plane obliquely inclined to the earth's axis. Slow changes
in the direction of this axis are invoked to provide an explanation of
the precession of the equinoxes. The second book of the De revolutionibus
deals with the elementary mathematical technique of astronomy and contains
a star catalogue based upon that of Ptolemy. The remainder of the work
is devoted to constructing geometrical schemes, or theories, specifying
in detail the motions of the earth (Book III), the moon (Book IV), and
the planets (Books V and VI). These schemes were based on recorded observations,
and they served for the computation of tables enabling the places of these
bodies in their orbits to be predicted for any future time. Moreover, Copernicus
was able, on the basis of his theory, to determine for the first time in
history the relative distances of the earth and planets from the sun. Copernicus
referred the planetary motions to the sun (or, more precisely, to the center
of the earth's orbit), and thus succeeded in greatly reducing the number
of independent circular motions which the older astronomers had been obliged
to postulate in order to account for non-uniformities in the rates of apparent
motion of the planets; Copernicus showed these to be merely optical consequences
of the single annual revolution of the earth. He retained, however, much
of the antique natural philosophy upon which the geocentric (or earth-centered)
cosmology had been founded; and in constructing the planetary orbits he
considered himself bound by the ancient convention that the heavenly bodies,
being by nature "perfect," must move at uniform rates in exact circles
or in curves compounded of such circular motions. This artificial restriction
and the inadequacy of the basic observations rendered the Copernican tables
of planetary motions scarcely more accurate than others of the period.
This deficiency was subsequently remedied by the refined observations of
Tycho Brahe and by Johann Kepler's reformulation of the Copernican theory
in accordance with more soundly based laws of planetary motion.
Copernicus' Editors
Some uncertainty as to the intention of the
Copernican theory was at first occasioned by the inclusion in the De revolutionibus
of an anonymous note addressed "to the reader" and declaring that the hypothesis
of the earth's motion was to be understood merely as a device to facilitate
the calculation of tables and not as a statement of physical fact. This
note was inserted, without authority, by Andreas Osiander, a Lutheran mathematician,
to whom Rheticus had handed over the task of seeing the book through the
press. The identity of the author was eventually revealed by Kepler some
seventy years later. Meanwhile the original manuscript of the De revolutionibus
had been lost; and it was not recovered until the 19th century, when it
was critically examined to determine the principal stages in its composition
and to date them by reference to recorded observations included in the
text. The manuscript bears no title: this must have been supplied by editors,
who also introduced considerable alterations into the text. These remained
unsuspected until Curtze brought out his critical edition of 1873, based
on the author's holograph.
Influence
The Copernican theory was opposed at first
by the Protestant leaders as being contrary to the teaching of Scripture;
and in 1616 it was declared erroneous, if not heretical, by the Roman Inquisition.
Galileo's advocacy of the new astronomy was silenced in 1633. A serious
scientific objection to the theory was that the annual revolution of the
earth about the sun should produce the appearance of a corresponding apparent
motion of the stars in the opposite direction, a phenomenon which the most
refined observation long failed to reveal. The reason for this apparent
anomaly is the great distance of the stars from the earth; the motion of
the stars was too small to be detected by the instruments of Copernicus'
time. Not until 1838 was the existence of such an annual parallax established.
Nevertheless, the theory secured general acceptance among leading astronomers
within a century and a half of its formulation. It was presupposed in Kepler's
enunciation of the fundamental laws of planetary motion (1609-1619), and
Newton in 1687 interpreted these laws as necessary consequences of a gravitational
attraction of the planets toward the central sun. During the 18th and 19th
centuries various attempts were made to prove, by observation or experiment,
the "truth" of the Copernican theory; but in the light of Einstein's principle
of relativity, any decision to regard one cosmic body as at rest and another
as moving is now seen to have no relation to any real distinction in nature
and to be justified only on considerations of convenience.
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Donati, Giovanni Battista (1826-1873),
Italian astronomer and discoverer in 1858 of Donati's Comet. He was the
first to examine the spectrum of a comet, and his investigation of Tempel's
Comet in 1864 proved that comets are self-luminous bodies.
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Eddington, Sir Arthur Stanley (1882-1944),
English astronomer, one of the greatest astronomers of modern times. He
was born in Kendal on Dec. 28, 1882, the son of Quaker parents. His father,
headmaster of a local school, died when Eddington was two. Educated at
Trinity College, Cambridge, Eddington received honors in mathematics in
1904 and was appointed chief assistant at the Royal Observatory, Greenwich,
in 1906. His practical work included longitude determinations at Malta
and an eclipse expedition to Brazil. His theoretical work on stellar motions
and star-drifts soon placed him among the ablest astronomers.
Already a fellow of Trinity and a Smith's
Prize winner, Eddington was appointed Plumian professor of astronomy and
head of the observatory at Cambridge in 1914. Shortly thereafter, he discovered
the fundamental role of radiation pressure in stellar equilibrium. Pioneer
research on the internal constitution of the stars -- in which he demonstrated
that the sun, though denser than water, is nevertheless gaseous -- and
the pulsation theory of cepheid variables followed; he formulated the mass-luminosity
relation in 1924. He early realized that the sources of stellar energy
must be subatomic and also that hydrogen is overwhelmingly the chief constituent
of the universe.
Having read Albert Einstein's paper on general
relativity, Eddington was the first and most distinguished exponent in
the English language of the theories of relativity and the first to confirm
from eclipse observations the gravitational deflection of light predicted
by Einstein (1919). He tried to develop a fundamental theory linking relativity
and quantum theory within the framework of the expanding universe, and
he deduced from these relationships all the cosmic and atomic constants
of nature. Unfortunately, this provocative attempt at a great synthesis
remained incomplete at his death.
Eddington was awarded five gold medals, was knighted
in 1930, and received the Order of Merit in 1939. He was a mystic in the
Quaker tradition, and this intuitive approach to truth also guided his
approach to scientific problems. He died in Cambridge on Nov. 22, 1944.
The principal works by Eddington include
Stellar Movements and the Structure of the Universe (1914); Report
on Relativity Theory of Gravitation (1918); Space, Time and Gravitation
(1920); Mathematical Theory of Relativity (1923); The Internal Constitution
of the Stars (1926); Stars and Atoms (1927); The Nature of
the Physical World (1928); Science and the Unseen World (1929);
The Expanding Universe (1933); New Pathways of Science (1935);
Relativity Theory of Protons and Electrons (1936); The Philosophy
of Physical Science (1939); and Fundamental Theory (posthumous,
1946). Works on Eddington include From Euclid to Eddington (1949),
by Sir Edmund Whittaker; Arthur Stanley Eddington (1956), by A. Vibert
Douglas; and Eddington's Fundamental Theory (1957), by N. B. Slater
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Flammarion, Camille (1842-1925),
French astronomer who believed that vegetable life existed on the moon,
that Venus rotated in a short period, and that Mars was inhabited. Flammarion's
book, La Planète Mars , became a standard work; he also revised
Messier's catalogue of nebulas and star clusters.
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Flamsteed, John (1646-1719),
English astronomer, was born at Denby, Aug. 19, 1646. He left school at
the age of 16 because of ill health and began his study of astronomy. From
his observations with a small telescope it became evident that the current
astronomical tables were deficient. Flamsteed's calculations of an eclipse
and lunar occultations gained him general scientific recognition by 1670.
In that year he entered Cambridge, taking his degree of M.A. in 1674. There
was then no good method of determining longitude at sea, and a commission,
including Flamsteed, reported that an observatory was needed to make observations
and new tables for navigation purposes. Charles II founded the Greenwich
Observatory in 1675 with Flamsteed as the first Astronomer Royal.
Flamsteed undertook enormous tasks: he constructed
a better catalogue of stars than any extant; began systematic observation
of the planets, moon, and sun; revised the theory of their motions; and
computed tables for future ephemerides. Although handicapped by ill health
and lack of adequate funds, he helped in the design and construction of
new instruments of observation and rationally determined and allowed for
their errors. Flamsteed was a pioneer in fundamental astronomy (for example,
his determinations of the obliquity of the ecliptic, the position of the
equinoctial points, and the right ascensions of stars) and revised and
improved the theory of the motions of the moon and of the planets Jupiter
and Saturn. His three-volume work -- finished by his assistants Joseph
Crosthwait and Abraham Sharp after his death -- Historia coelestis Britannica
(revised edition, 1725) contained Flamsteed's observations and catalogue
of about 3,000 stars. It was the Royal Observatory's first great service
to science. He died in Greenwich on Dec. 31, 1719
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Galileo Galilei. (1564-1642),
Florentine physicist, philosopher, and inventor, whose name became the
cardinal emblem of Renaissance science and of the ensuing technological
revolution. He was born in Pisa, Feb. 15, 1564. His family, which had been
a powerful one in the affairs of Florence during the previous century,
had declined in influence and wealth, and Galileo's father, Vincenzio,
an able mathematician and musician, found his numerous family -- Galileo
was the eldest of seven -- difficult to support. At the age of twelve,
Galileo was sent to a nearby school at Vallombrosa, where he followed
the usual course of studies in Latin, Greek, and logic, and for a time
thought of joining the religious order which administered the school. In
1581, he entered the University of Pisa and began the study of medicine.
He soon tired of this; already proficient in music and painting, he now
turned to the other side of his paternal inheritance and -- to the father's
dismay, it is recorded -- became absorbed in mathematics. After four years,
he was forced by lack of means to leave the university without graduating;
his formal education ended, therefore, when he was just twenty-one. Galileo
continued his researches in private, and in 1586 wrote an account of a
hydrostatic balance (bilancetta) accurate enough to have solved Archimedes'
famous assay problem (testing the purity of a gold coronet). He was fortunate
enough to attract the attention of a wealthy patron, the Marchese del Monte,
and wrote for him a treatise on centers of gravity (1588). In the following
year, his patron managed to have him appointed a lecturer in mathematics
in his old university. Here he remained only two years; his teaching appears
to have aroused considerable opposition. Shortly after he rejoined his
family, now living in Florence, his father died, leaving him to fend for
the others; he was to support them for many years.
In 1592, his patron managed to have him
appointed to the nearby university at Padua, where he remained for eighteen
years, the happiest and busiest period of his life. At Padua, two centuries
of steady development had fused the fertile Ockhamist and Averroist traditions
of thirteenth-century Oxford and Paris; the discussions of Grosseteste,
Buridan, Albert of Saxony, Swineshead, Oresme, and d'Ailly, which had led
to important modifications in Aristotelian science -- especially in the
areas of mechanics and optics -- were continued by the great fifteeth-century
Paduans, Paul of Venice, Cajetan of Thiene, and Johannes Marlianus, thus
making Padua the leading center of the day in natural philosophy. Galileo
had been aware of the non-Aristotelian "impetus" mechanics even while at
Pisa, as an early unpublished and still quite "Aristotelian" treatise (1590)
of his on motion shows. But it was at Padua that he was to glean most of
the intellectual riches later to be turned to such good account. Here he
began his experimental work on mechanics, inspired perhaps by Marlianus
who had already been rolling balls down inclined planes and testing pendulums
more than a century before in Padua; he wrote much but published nothing
except a couple of short papers (1606-1607) on an ingenious device somewhat
like a slide-rule.
In 1609, he heard that a Dutch emissary
was trying to interest the rulers of Florence and Venice in an optical
instrument which made distant things seem close by. (Crude telescopes had
already been on sale for about a year in Holland; della Porta in his Natural
Magic [1582] had adumbrated such an instrument nearly thirty years
before.) Galileo set to work to construct one; his knowledge of optics
was enough to show him roughly what form it would have to take. In a few
days, he had one ready; upon his demonstrating it to the appreciative senate
of Venice (August 1609) they forthwith doubled his salary and gave him
permanent tenure. During that winter, he turned his telescope to the skies
with startling results, some of which were communicated to the world in
the Sidereus nuncius (1610), the work that made him famous all over Europe.
He announced that the moon's surface is quite similar to that of the earth
-- irregular and mountainous; that the Milky Way is made up of a host of
stars; and that the planet Jupiter is accompanied by at least four satellites.
Soon afterwards he discovered that the planet Venus has crescent phases
just as the moon has, and that variations in observed planetary brightness
(presumably a measure of planetary distances from the earth) were much
greater than had been supposed. The electrifying effect of these discoveries
on contemporary thought is hard for us to appreciate today. They showed,
first, that the human senses could be aided artificially to discover new
truths about nature, something that neither philosophy nor theology had
previously had to contend with; second, that the central tenet of Aristotelian
cosmology -- that the heavenly bodies are made of a clear "aethereal" substance
whose characteristic movement is circular and eternal -- could not be maintained;
third, that the Ptolemaic astronomical model, which made the planets revolve
around the earth, was untenable. (It could not explain how Venus is sometimes
between sun and earth, sometimes further away.) Unfortunately the new observations
did not -- and could not -- decide between the rival models of Copernicus
and Tycho Brahe. Tycho had suggested that the planets revolve around the
sun, and the sun in turn around the earth. These two models were, in fact,
exactly equivalent from the kinematic, or descriptive, point of view.
At this point, Cosimo de' Medici invited
Galileo to return to Florence as Mathematician Extraordinary to the Duke,
with no teaching duties and a large salary. To the dismay of his Venetian
benefactors, Galileo gratefully accepted this honor. He brought with him
his three illegitimate children, two girls and a boy, and married off their
somewhat tempestuous Venetian mother to one of her own countrymen. The
girls he ultimately placed in a nearby convent in Arcetri, although he
had to get a dispensation to do so since they were too young to enter in
the normal way. In 1611 Galileo visited Rome. Feted by cardinals and princes,
he spent sev eral triumphant months demonstrating his new discoveries.
On his return, he began to observe the sunspots systematically, and although
both Fabricius and Christopher Scheiner, S.J., had published papers on
this topic before Galileo's Letters on Sunspots appeared (1613), it seems
possible that Galileo had been, in fact, the first to use the telescope
for this purpose. (He was later to claim that he had been "the first discoverer
of the solar spots as well as of all other celestial novelties.") The Letters
confirmed his earlier criticism of Aristotelian cosmology.
But by now a groundswell of opposition to
his views was beginning to grow among the Aristotelian philosophers. Although
he had not as yet committed himself in his writings, he was well known
to be a supporter of "realist" Copernicanism, i.e., the view that Copernicus'
heliostatic model was not only the most convenient mathematical way of
describing planetary motions, but also, as Copernicus himself had believed,
the "true" view of the universe. His opponents concentrated upon the weaknesses
of Copernicanism -- in particular, its apparent opposition to Scripture
-- rather than upon the defense of the Aristotelian dynamics, already under
severe attack for several centuries. Galileo responded by writing two letters
for publication, one to his pupil Castelli and the other to the Dowager
Duchess Cristina, in which he argued that the biblical writers had to express
themselves according to the physical views of their day in order to be
understood; that they admittedly made much use of metaphor, e.g., in speaking
of God; that they were principally concerned with questions of human salvation;
that the Fathers gave no explicit witness in favor of a literalist interpretation
of the disputed passages; that God has revealed Himself in two ways to
man, through Revelation and through Nature, and that since these two ways
must necessarily harmonize, the proper way of approaching the latter is
through unhampered scientific reasoning. In stating his conclusion, however,
he bowed to theological tradition. Instead of holding that in matters of
science the biblical modes of expression have no particular authority --
the conclusion towards which his reasoning certainly pointed -- he argued
that the literalist interpretation of a biblical passage must be maintained
unless it is "manifestly demonstrated" from some other source that this
leads to falsehood.
When these letters were published, they
caused uncomfortable stirring in Rome. But their final conclusion did not
seem to contradict the opinion expressed by Bellarmine, then the leading
Roman theologian, that if a "real proof" of the earth's motion were given,
the literalist interpretation of the biblical passages concerned would
have to be modified accordingly. Bellarmine added ambiguously that as no
such proof was forthcoming, "in case of doubt, one may not abandon the
Scriptures....." Thus, despite the attempts of Galileo's enemies to
make capital of these letters, no action was taken. Galileo was alarmed,
however, by the news from Rome, and decided to present his views personally
there (December, 1615).
Whether his trip to Rome precipitated the
ultimate crisis or not is debatable; in any event, a few months later a
committee of consultors of the Holy Office (the "Inquisition," or congregation
in charge of matters of faith) declared that in their opinion the proposition
that the sun is the immovable center of the universe was heretical, whereas
the proposition that the earth moves was theologically "erroneous." (By
calling the former proposition "heretical," the committee meant that it
contradicted Scripture and thus implicitly called in question the defined
Catholic dogma of the divine inspiration of Scripture; but the proposition
that the sun moves had not been at any time declared a dogma.) The Holy
Office then entrusted Bellarmine with the task of admonishing Galileo to
abandon "realist" Copernicanism, while Copernicus' book was put on the
Index until it could be "corrected." (A few "realist" phrases were, in
fact, deleted and the book was reissued four years later.) Galileo returned
to Florence, dejected but not altogether disconsolate. He was still allowed
to discuss the Copernican view as a mathematical device, but not as a possible
cosmology.
In 1618, a dispute about the nature of comets
broke out, this time between H. Grassi, a leading Jesuit astronomer, and
Galileo (writing first through his disciple Guiducci). Grassi held that
comets are solid bodies outside the lunar orbit, whereas Galileo argued
that their appearance is caused by some sort of trick of refraction in
the earth's atmosphere. Though Grassi's contention was essentially correct,
he relied overmuch on historians and early philosophers; Galileo in Il
Saggiatore (1623; The Assayer ), one of the masterpieces of Italian
literature, was thus enabled to heap ridicule on his opponent's head, without
meeting his main argument.
By polemics of this kind, Galileo gradually
alienated the Jesuit astronomers, once his strongest support. Il Saggiatore
was dedicated to his friend Cardinal Maffeo Barberini who had just been
elected pope and had taken the name Urban VIII. Galileo went to Rome to
visit him and was well received; despite his best efforts, however, he
failed to obtain a rescinding of the Holy Office's decree of 1616. Neverthe
less, he was led to believe that he could discuss Copernicanism "hypothetically";
it was unclear whether "hypothetically" meant "as a convenient mathematical
device for describing the phenomena" (the usual sense of "hypothesis" at
that time), or "as a permissible claim about the real state of things."
Galileo adopted the latter interpretation.
In 1630, he completed the work he had been planning for
so long, the Dialogue Concerning the Two Chief World Systems , in which
he deals with the Copernican and Aristotelian-Ptolemaic models. It is assumed
that these are the only models -- Tycho Brahe's alternative is not mentioned
-- and the Dialogue comes down heavily on the side of Copernicanism, understood
in "realist" fashion. There followed a lengthy and complicated wrangle
with the Roman censors which lasted almost two years. The chief censor,
Riccardi, a friend of Galileo's, was caught in a very difficult position.
His instructions were far from clear; Urban seemed to have permitted a
"hypothetical" interpretation, yet the Dialogue clearly appeared to contravene
the decree of 1616. Riccardi kept making minor changes and delaying a final
decision; in the end, his consent was "dragged" from him, as a Roman friend
of Galileo's put it, and the book was printed in Florence (1632).
A book like the Dialogue was bound to be
suspect, unless and until the 1616 decree was rescinded. It had scarcely
appeared, indeed, before trouble began. Urban was furious, feeling he had
been tricked; the edition was confiscated and its author summoned. Galileo
delayed, but stern threats brought him to Rome by the following February
(1633). His trial before the Holy Office did not begin until April; he
was permitted to stay at the Tuscan embassy throughout the trial except
for one period in a Vatican apartment. This unusual treatment is typical
of the gingerly way in which the trial as a whole was conducted. The examiners
sent to read the book reported that it did indeed defend "realist" Copernicanism
quite openly. Galileo denied this, saying -- rather implausibly
-- that he had really argued against Copernicanism. Later, he admitted
that parts of the book were an explicit defense of Copernicanism, but claimed
that he himself since 1616 had never believed nor defended this doctrine.
The sentence was not handed down until June; it declared that Galileo by
his writing had rendered himself "vehemently suspect of heresy" because
of his defense of "realist" Copernicanism. Galileo was forced to abjure
this doctrine publicly, and was sentenced to imprisonment; this was informally
commuted to permanent house arrest.
Galileo was removed to the home of his friend
the archbishop of Siena, where he spent the next six months, and resumed
the work on dynamics he had broken off twenty years before. In December
he returned (still under house arrest) to his villa at Arcetri near Florence;
a few months later the light of his life, his gentle daughter, Sister Maria
Celeste, died. He continued his writing, however, and in 1636, his greatest
work, the Discourses Concerning Two New Sciences , was ready. He sent it
abroad; it got an imprimatur in Vienna but was eventually published in
Holland. The first part treats of the properties of solid bodies; the second
deals with accelerated motion in general and that of projectiles in particular.
Much of what the book contained was already well known by word of mouth
from Galileo's pupils, but the book served as a final compilation of his
thoughts on many diverse problems in physics. It had a tremendous influence
on the growth of physical science in the decades that followed. After its
appearance, Galileo made his last observational discovery, the libration
(a slight apparent rotational variation) of the moon. In 1637 his eyesight
began to fail, and in 1638 he went blind. More and more visitors came to
see the old man; he was surrounded by worshiping pupils like Viviani and
Torricelli. He continued to work on some appendices for his book, as well
as on experimental problems, but in 1641 his health gave way; he died on
Jan. 8, 1642. Galileo was buried in his own church of Santa Croce; it was
not until much later that permission was given to erect a monument over
the great scientist's tomb.
Implications of the Trial
The legality and implications of his trial
have been endlessly debated. There can be no doubt that personal animosities
against Galileo played some part in its happening at all. Galileo had received
permission from the censors to print the book; this was clearly his chief
defense. Against this, the prosecution alleged that the censors had been
unaware of a secret injunction given Galileo by Bellarmine in 1616, ordering
him not to defend Copernicanism in any manner whatsoever. The record of
this injunction was produced. Much of the controversy about the trial has
centered around the authenticity of this document. It has been claimed
to have been a forgery, or at least to have been enjoined illegally upon
Galileo. The evidence for this claim, though significant, remains inconclusive;
the argument rests in part upon a doubtful reading of a key phrase. The
grounds for the 1633 trial must, in the last analysis, be sought in the
1616 decree. When the examiners declared in 1616 that the doctrine of the
sun's being at rest impugned the inspiration of Scripture and was
therefore formally heretical, the die was cast.
Behind this declaration lay a serious ambiguity.
"Certain" proof of a proposition's falsity had to be given before a literalist
interpretation of Scripture which seemed to imply this proposition could
be officially relaxed. But what was to happen before a certain proof was
available? Would a highly probable proof have no standing at all? Could
a scientific theory ever in fact become "certain" in the sense intended
here by Bellarmine? Furthermore, it was generally realized by philosophers
of the time that a kinematic astronomical model (one which left out of
account all questions concerning the causes of motion) could not possibly
furnish a certain proof, or even a probable one, as to which of two bodies
in motion relative to one another was the one "really" moving. Aristotle
in his astronomy had discussed the causes of motion, as Newton would later
do, but Copernicus' model was purely kinematic, just as Ptolemy's had been.
Galileo was forced, therefore, to look for a nonastronomical argument for
the "reality" of the earth's motion, and the one he chose (based on an
analysis of tidal motion) turned out to be a broken reed.
If the Holy Office had realized in 1616
that the legitimacy of taking a literalist interpretation of some biblical
passages would become more and more problematic as science posed a progressively
greater challenge to such an interpretation, it might have permitted Galileo
to argue for "realist" Copernicanism as long as he did not claim for his
argument a greater certainty than it had. The approach the Church follows
today is that science and theology each have their own method, that when
a problem common to both -- the origin of man, for example -- arises, each
is assumed to have something to say on the matter, and that therefore each
ought to listen to the other with respect. This does not mean that science
and theology are regarded as completely unrelated and incapable of clashing
since the results of one may well circumscribe the other. But such conflicts
have in fact become rarer as the competence and limits of each relative
to the other have been better defined. In the period just after the Reformation,
however, both Catholics and Protestants were abnormally sensitive about
any new suggestion of a restriction on the meaning of biblical passages
for which a literalist interpretation had been traditionally accepted;
and Galileo did make such a suggestion. Galileo's alienation of potential
supporters by his quarrels over priority of discovery and by his sarcasms
made matters worse, while his lack of "certain" proof of the earth's motion
provided an easy target.
Galileo's Importance
In assessing the impact of Galileo Galilei upon the history
of ideas, one must distinguish between Galileo the symbol and Galileo the
scientist. For many, Galileo became the symbol of the revolt of reason
against the blind forces of authority and ignorance, of the clear certitudes
of science against the murky opinions of medieval philosophy and theology.
Legends by the dozen grew up around him. (It is unlikely, according to
recent research, that the familiar stories of Galileo's discovery of the
pendulum principle by timing the swinging lamp in Pisa Cathedral, or dropping
the balls from its Leaning Tower, or muttering "And yet it moves" as he
left the Minerva after his condemnation, have a solid foundation in fact.)
Galileo appears either as a villain, whose inordinate vanity precipitated
the whole crisis and whose contribution to science was as a publicist rather
than a scientist, or more often as a hero, beset on all sides by villains
of deepest dye, battling against an obscurantist attitude towards science
on the part of his opponents, and victim in his trial of an unscrupulous
plot. The truth is, as usual, much less black-and-white than either of
these extreme views would imply.
Galileo's principal contributions can be
summarized under five headings. First, he provided practical instruments
which gave a new reach and accuracy to science. The principles underlying
these -- the telescope and the thermometer, for example -- were already
known to some extent, but he converted into efficient instruments of science
what had formerly been mere curiosities. He realized the fundamental importance
of the accurate measurement of short time-intervals and suggested ways
of doing this, one of which led ultimately to the pendulum clock; he improved
the microscope and the geometric calculator, and laid the groundwork which
ultimately led his pupil Torricelli to the discovery of the barometer.
The second area of science to which Galileo
contributed was that of qualitative astronomy. It was he who first publicized
the discoveries that the telescope had made possible and underlined their
theoretical importance. He inferred from them, correctly, that the same
type of mechanics should govern matter in all parts of the visible universe,
and that the geocentric astronomical model of Ptolemy and Aristotle could
no longer be defended. Galileo was never interested in positional measurements,
the classical data of astronomers; he cannot be ranked in positional astronomy
with his contemporaries, the theoretician Kepler, and the observer Brahe.
It is ironic that Kepler appears to have sent him a copy of his New Astronomy
(1609), in which the elliptical character of Mars' orbit was for the first
time shown; in addition, Kepler suggested an "attraction" between sun and
planet as an explanation of planetary motion. Galileo explicitly rejected
the notion of attraction. He never seems to have questioned his own theory
of planetary motion (that a planet moved "naturally" in a circle because
this is the only stable figure for perpetual motion).
His third important contribution was his
trenchant criticism of various aspects of the Aristotelian theory of motion.
There was little in his critique that had not been anticipated, to a greater
or lesser extent, by some of Aristotle's own commentators (like Philoponus
in the sixth century) and especially by the Ockhamists of fourteenth-century
Paris and by his own Paduan predecessors in the sixteenth century. He criticized
the Aristotelian "laws" of motion, notably the one which made velocity
in free fall proportional to weight, pointing out that it did not (and
indeed could not) accord with experience. He rejected, besides, the whole
theory underlying Aristotle's treatment: the assumption that whatever is
moving is being actively moved by something else, the dichotomy between
celestial and terrestial movements, and the notion of four "elements,"
each with a particular sort of "natural" up-or-down motion. He could then
logically reject Aristotle's claim that the earth, composed of the heaviest
element, must be at the center of the universe. Even though his criticisms
were not novel, they were expertly marshaled, and relied upon an extremely
effective blend of experimental evidence and proofs of the logical inconsistency
at crucial points of the older system. As Galileo himself remarked, the
Aristotelians of his day had lost the feel for experience that had characterized
their master. The enthusiasm for ancient texts and the worship of long-dead
thinkers, which were such prominent features of the Renaissance, affected
philosophy too; the growth of physics in the universities had slowed down
in consequence. Galileo's criticisms, with their wit and incisive logic,
thus had a devastating effect.
Fourth came Galileo's positive contributions
to systematic science. Most of these were contained in his Discourses,
which corrected and replaced many of the earlier, cruder views of the Dialogue
and of his youthful unpublished work, On Motion . In the Discourses, one
finds discussions of such diverse topics as the method of virtual velocities
for the solution of statical problems, acoustical patterns on metal plates,
the production of vacuums, the possibility of a finite velocity for light,
and the breaking stress of beams. But above all, the Discourses contained
the beginnings of the new mechanics: it enunciated the notion of acceleration
(adumbrated in the work of earlier writers like Oresme, Da Vinci, and especially
Soto) in a clear fashion, indicating how acceleration ought to be measured;
it gave the law of free fall (distance varying as the square of the time);
it indicated a method of compounding two simultaneous motions, something
the Aristotelians had always rejected on theoretical grounds; it suggested
a form of the principle of inertia and a rough version of the principle
of conservation of momentum; it used all of these insights to solve the
long-existing problem of projectile motion.
Galileo argued that if the resistance of
the medium to a moving body be reduced to zero (or if, equivalently, the
"ideal" case of a vacuum be considered), the "impetus" would remain constant.
The body would, therefore, continue in motion. The classical impetus theory
of Buridan and Oresme thus indirectly prepared the way for this all-important
new step. Impetus is no longer introduced to explain motion, only to describe
it, while uniform motion is taken to need no continuing cause. This represents
a great step from the Aristotelian view toward Newton's first law of motion.
The most vexing problem in assessing Galileo's
contibution to thought is the extent to which he introduced a new "scientific
method." The reaction against the sterility of the Aristotelian science
of the 16th century was such that many of the pioneers of the "new" science
(Bacon and Descartes even more than Galileo) insisted that theirs was an
entirely new "method." It is not clear that Galileo himself really believed
this, although in his works he sometimes gives this impression.
Galileo insisted upon the primacy of theoretical
insight in science; he thought of experiment primarily as a means of convincing
others rather than as a means of reaching those fundamental (to him) "causes,
which are not revealed by experiment." He frequently relied upon imaginary
"experiments" to illustrate points he knew "must" be true. His law of falling
bodies was reached in purely theoretical fashion; his inclined-plane experiments
not only did not furnish its original basis, but (as Mersenne was to point
out) could be said to "confirm" it only in the broadest sense. He praised
Copernicus for following his astronomical insight and ignoring the major
discrepancies between his model and the observed brightnesses of the plants;
he himself backed this model as the "true" account, although he must have
known that from the purely experimental point of view it was indistinguishable
from that of Tycho. The principal argument he adduced for the Copernican
view had no experimental basis, and was in conflict with the evidence of
the well-known correlation of the tides with the lunar periods.
Though he was not an "experimentalist" in
the modern sense, he emphasized the importance of experiment, i.e., of
controlled observation, in areas where prior insight was lacking. Distrusting
casual observation, he invented new instruments for "putting Nature to
the question." Furthermore, he emphasized that these results ought to be
expressed mathematically (in effect, geometrically) since this permitted
manipulation and verification of a kind not hitherto achievable, and, in
particular, facilitated the accurate formulation of vital concepts like
acceleration and momentum that the earlier Paris physicists had in vain
tried to systematize. His conviction that "mathematics is the language
of Nature" led him to formulate not only laws in this way, but also to
predict that the inner structures of matter ought to be expressed mathematically
rather than in terms of intrinsic capacities (i.e., qualities). This view
led him to hold that matter is composed of atoms whose shapes and motions
are entirely describable in mathematical terms; his clear realization of
the scientific infertility of the earlier qualitative approach led him
to go further and treat qualities -- especially sense-qualities -- as totally
illusory.
Galileo's most important contribution to
scientific methodology may have been his knack of idealizing a problem,
of prescinding from experimental factors not immediately relevant or easily
controllable, of reaching "laws" that did not describe the motion of any
actual body; instead they said what the behavior of the body would be were
the influence of environment either eliminated or standardized. This went
counter to Aristotle's assumption that a body had to be observed in its
normal environment to learn what its "natural" activity was, but it permitted
Galileo to transcend observational complexities that would have made it
impossible for him to reach the simple form of the laws of motion he aimed
for. His predecessors had been preoccupied with the causes of motion; he
bypassed this problem almost entirely, insisting that an accurate description
of motion had to come first. It was Newton who later solved this problem
-- in interim fashion, at least -- by reintroducing causes or forces, and
giving them an operational definition.
Galileo thus brought to focus a number of
disparate elements of method that had been present, some clearly, some
obscurely, in the tradition he inherited at Padua. This enabled him to
launch an effective attack on some of the central tenets of Aristotelian
physics, and at the same time to replace these with a preliminary systematic
account of his own. In addition, his great gifts of exposition brought
these advances home to people in a manner, and at a rate, that was distinctly
new.
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Henderson, Thomas (1798-1844),
Scottish astronomer who catalogued the declinations and right ascensions
of 172 fixed stars in the southern hemisphere. He refined the measurement
of lunar parallax and was the first to measure the parallax of Alpha Centauri.
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Herschel, Sir William (1738-1822),
British astronomer, was born Friedrich Wilhelm at Hannover, Germany, Nov.
15, 1738. He had little schooling but was possessed by a desire for learning
and became one of the greatest astronomers of his time. For years, however,
he was a musician in the Hanoverian Guards. He went to England in 1757
and was a music teacher and organist by day and followed his hobby of observing
the stars at night. During his nocturnal survey of the heavens on Mar.
13, 1781, Herschel discovered the planet Uranus, and for this discovery
he immediately became famous. George III made him king's astronomer. He
constructed many telescopes, including a 20-foot (6.1-meter) and a 40-foot
(12.2-meter) reflector. These enormous instruments were erected at his
home in Slough and became world-famous.
Herschel was an indefatigable worker. For
many years he made nightly systematic surveys of the sky, examining planets,
stars, nebulae, and star clusters. By day he worked over his results or
directed the construction of his telescopes. His sister Caroline was his
assistant and became an independent worker of some standing. Herschel observed
sunspots, confirmed the gaseous nature of the sun, rediscovered the Martian
polar caps, and believed in the possibility of life on Mars. He announced
the trade-wind theory of Jupiter's belts and discovered two of Jupiter's
and two of Uranus' moons. His principal work was on stars, and it was in
this field that he made two discoveries of primary importance: the movement
of the solar system through space, and the evidence that binary stars move
around a common center of gravity. This evidence substantiated the universality
of Newton's theory of gravitation. Herschel discovered nearly 1,000 double
stars. In 1785 he brought out the disc theory of the stellar system, holding
that all nebulae are clusters of stars, which he called island universes.
He abandoned the idea of the Milky Way as a collection of stars uniformly
distributed and came to believe that it was composed of local groups and
clusters. The nebulae, he thought, were all clusters not yet resolved into
stars. Herschel also discovered from 2,000 to 3,000 nebulae and clusters
on which he published catalogue reports. After years of profound research
he brought out an important paper on the construction of the heavens, theorizing
on the evolution of matter by successive steps from nebulous material to
the final planetary state, by means of gravitation. Herschel died at Slough,
England, Aug. 25, 1822.
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Hertzsprung, Ejnar (1873-1967),
Danish astronomer and engineer, discovered the relationship between the
color of a star and its absolute brightness. This relationship, distinguished
independently by Henry Norris Russell, is the basis for the Hertzsprung-Russell,
or H-R, diagram, which is one of the fundamental tools of stellar astronomy.
Hertzsprung also derived the relationship between a star's spectrum and
its absolute brightness, a relationship that permits an estimation of the
star's absolute magnitude from the appearance of its spectrum.
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Hubble, Edwin Powell (1889-1953),
the American astronomer who was the first to provide observational evidence
for the expansion of the universe, was born in Marshfield, Mo., on Nov.
20, 1889. He was educated at the University of Chicago, where the
astronomer G. E. Hale inspired him with a love of astronomy, and also at
the University of Oxford. Later he held posts at Mount Wilson and Palomar
observatories. He concentrated on the study of nebulae, particularly extragalactic
nebulae. In 1923 he detected a Cepheid variable star in the Andromeda nebula,
a discovery that enabled him to estimate the distance of the nebula. As
a result, it was clear that spiral nebulae are galaxies, that is, independent
systems of stars lying outside the Milky Way. Hubble introduced a system
of classification of galaxies and studied their distribution and their
line-of-sight (radial) velocities. He found that most galaxies are receding
and that there is a linear relationship between radial velocity and distance.
He also showed that their distribution throughout space is fairly uniform.
These results are fundamental in modern cosmology. Hubble's books The Realm
of the Nebulae (1936) and The Observational Approach to Cosmology (1937)
made his discoveries widely known. Hubble's great achievements were widely
recognized during his lifetime by the many honors conferred upon him. He
died in San Marino, Calif., on Sept. 28, 1953.
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Huggins, Sir William (1824-1910),
English astronomer who was the first to use a spectroscope to study individual
stars in detail. His major achievements included the invention of a method
of determining the motion of a star by the shift in its spectral lines
and the recognition of the gaseous, rather than stellar, nature of certain
nebulas.
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Jeans, Sir James Hopwood (1877-1946),
British mathematician, physicist, and cosmogonist, widely known for his
theory of the creation of the solar system. He was born in Ormskirk, Lancashire,
on Sept. 11, 1877. In 1900 he was graduated from Trinity College, Cambridge.
His graduate research was interrupted by tuberculosis, of which he was
cured after two years of sanatorium treatment. In 1906 Jeans was elected
a fellow of the Royal Society of London. From 1919 to 1929 he held the
influential honorary secretaryship of the society. He was president of
the British Association for the Advancement of Science in 1923-1924 and
of the Royal Astronomical Society in 1925-1927. With Sir Harold Jeffreys,
Jeans is the author of the tidal hypothesis of the origin of the solar
system.
Jeans' scientific works include Dynamical
Theory of Gases (1904); Theoretical Mechanics (1906); Mathematical Theory
of Electricity and Magnetism (1908); Problems of Cosmogony and Stellar
Evolution (1919, based on an Adams Prize essay, 1917, Cambridge);
The Nebular Hypothesis and Modern Cosmogony (1922); and Astronomy and Cosmogony
(1928).
About 1925 Jeans gradually turned his efforts from original
technical research to more popular writing, which gained him wealth and
worldwide fame. Among the most noted of these books are The Mysterious
Universe (Rede Lecture, Cambridge, 1930), in which he concluded that
God is a pure mathematician; The Universe Around Us (1929); The Stars in
Their Courses (1931); and Eos, or the Wider Aspects of Cosmogony (1929).
Later his thoughts turned to philosophy, in which field he wrote The New
Background of Science (1933); and Physics and Philosophy (1942).
Jeans made vital additions to the great
problems of cosmogonic theory; his last outstanding discovery, in 1926,
was that of the radiative viscosity in stars. In addition his popular lectures
and books stimulated and instructed a wide public. His philosophical writings,
and those of his contemporary, Eddington (with whom he had famous controversies
on astronomy), were attacked by some professional philosophers, partly
for their deistic tone -- which, however, won much public and ecclesiastical
favor. Jeans died in Dorking, England, on Sept. 16, 1946.
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Jeffreys, Harold (1891-1989),
English geophysicist and astronomer, was born Apr. 22, 1891, in Fatfield,
Durham. He was educated at Armstrong College, Newcastle-on-Tyne, and St.
John's College, Cambridge. After a brilliant scholastic record he became
a fellow of St. John's in 1914, and from 1946 to 1958 was Plumian professor
of astronomy and experimental philosophy at Cambridge University. Jeffreys
was one of the world's leading authorities on geophysics and wrote many
papers on cosmogony. With the Dutch astronomer Willem de Sitter he derived
the earth's oblateness by precession methods. He made a precise measurement
of the moon's shape, calculated the energy of tidal friction exerted upon
the earth's shores, and made extended researches on George Darwin's tidal
evolution theory of the earth-moon system. With Sir James Jeans, Jeffreys
was author of the tidal hypothesis of the origin of the solar system. He
proposed a modification (the collision theory) whereby an actual collision
of the sun and a star had occurred. His book The Earth: Its Origin, History,
and Physical Constitution (6th ed., 1976) is an authoritative statement
of geophysics. He also wrote on mathematics and mathematical physics. Jeffreys
was knighted in 1953. He died in Cambridge on Mar. 18, 1989.
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Kepler, Johannes (1571-1630),
German astronomer, whose epoch in the history of the physical sciences
ranks between those of Copernicus and Newton, symbolizing a transition
from ancient to modern times. He was born on Dec. 27, 1571, in Weil (at
that time a free city of the Holy Roman Empire and later of the kingdom
of Württemberg). Frail health destined him early to the career of
a scholar. After leaving the convent school of Adelberg monastery, he entered
the Swabian University of Tübingen in 1589, where he spent three years
studying theology, mathematics, and philosophy. Astronomy seems to have
at first played a subordinate role in Kepler's education, although at Tübingen
he received from Michael Mästlin an introduction to Copernican astronomy,
the defense and propagation of which became one of his great tasks. Kepler
intended to devote himself to the service of the Protestant church, but
his independence and lack of orthodoxy led his teachers to recommend him
as a professor of mathematics at the Academy in Graz (Upper Styria). This
was Kepler's first professional position, and it deflected his career to
astronomy.
His first work, a booklet entitled Prodromus
Dissertationum Cosmographicarum seu Mysterium Cosmographicum (1596), shows
its author attempting a quantization of planetary orbits, which proved
eventually to be altogether on the wrong track. The originality and boldness
of its approach, however, revealed such talent as to attract the attention
of the great Tycho Brahe, who invited Kepler to join him at the Benátky
Castle near Prague as a collaborator in his efforts to interpret theoretically
the planetary observations accumulated by Tycho during his lifetime.
Kepler joined Tycho in January 1600. This memorable
conjunction of the two leading astronomers of their time -- the aging,
great observer and the brilliant young theoretician -- lasted only
22 months before Tycho's death on Oct. 24, 1601. Kepler, however, was rapidly
reaching the zenith of his career. Such was the impression he created in
Prague that, only a few days after Tycho's death, Rudolph II named him
to succeed Tycho as Imperial Mathematician -- a position Kepler held, in
fact or in name, for the rest of his life.
The ensuing decade at Prague (1602-1612)
proved to be the height of Kepler's career. Patient efforts to fit the
apparent positions of the planet Mars, as observed by Tycho, to the various
current world-systems (Ptolemaic, Tychonic, Copernican) led Kepler
eventually to the empirical discovery of the planetary laws bearing his
name and constituting -- as is now known -- the integrals of the motion
of two bodies in inverse-square force field (a problem solved mathematically
by Newton at the close of the century). The first two of these laws, stating
that (1) the planets revolve around the sun in ellipses, with the central
luminary situated in their focus and (2) the radius-vector of each planet
sweeps equal areas in equal times, appeared in Astronomia Nova ....
(1609). This was Kepler's masterpiece and without doubt one of the most
important books on astronomy ever published, ranking with Copernicus' De
Revolutionibus and Newton's Principia. To be sure, the idea of the
heliocentric system itself had been proposed in antiquity by Aristarchus,
who believed that the planets revolve around the sun in circles at uniform
speeds. This led to discrepancies with the observations (caused by the
eccentricities of planetary orbits), which Ptolemy attempted to remedy
by inventing a whole system of geometrically complicated and physically
meaningless eccentric circles and epicycles. Fourteen centuries later,
Copernicus attempted to graft some of the Ptolemaic geometry (eccentric
circles) on the system of Aristarchus; but even for him the motions of
the planets still had to be uniform and circular. It was left for Kepler
to recognize the orbits for what they are -- ellipses, on which the planets
revolve with an angular velocity inversely proportional to the square of
their distance from the sun. These laws were entirely adequate for an interpretation
of Tycho's data within the limits of his observational errors; and such
small deviations as were discovered later are fully explained by Newtonian
mechanics.
Kepler himself movingly expressed his awareness
of the magnitude of his achievement and of the vistas opening before astronomy:
"Eighteen months ago, the first dawn rose for me; three months ago, the
bright day; and a few days ago, the full sun of a most wonderful vision;
now nothing can keep me back..... Well then, the die is cast. I am
writing this book for my contemporaries or -- what does it matter? -- for
posterity. Has not God himself waited 6,000 years for someone to contemplate
his work with understanding?"
The publication of his laws stirred little
interest in the scientific world for many decades and their significance
was fully realized only at the time of Newton. Kepler himself anticipated,
incidentally, that elliptical motion might be a consequence of a force
acting as the inverse square of the distance; but, not equipped with the
analytical methods of infinitesimal calculus, he was unable to prove it.
The proof had to await the advent of the calculus and Newton.
The publication of Astronomia Nova
and the almost simultaneous invention of the telescope make the year 1609-1610
a dividing line between ancient and modern times. They also mark the culminating
point in Kepler's life, both scientific and personal. After the death of
Rudolph II in 1611, Kepler found his position at the court in Prague increasingly
uncertain and the payment of his salary even more irregular. He therefore
obtained permission from the new monarch, Matthias, to accept temporarily
a post as provincial mathematician at Linz, in Upper Austria -- where,
in fact, he was to spend the next 15 years.
Kepler's principal scientific achievement at Linz was
the publication of De Harmonice Mundi (1619), containing the statement
of the third and last of his planetary laws -- that the squares of the
orbital periods of the planets bear the same ratio to each other as the
cubes of the semimajor axes of their elliptical orbits. Thereafter he worked
for nine years to complete the tables of the planetary positions, based
on his new laws of their motion.
Meanwhile, in the gathering storm of the
Thirty Years' War, religious intolerance and other vicissitudes forced
him to change his assistants, his printer, and even his abode several times.
During the last decade of his life he wandered through the imperial lands
in quest of a temporary haven or a new patron willing to engage the Imperial
Mathematician for pay as an astrologer. This superstitious preoccupation
at times gave rise to despondency, from which he tried to emerge by contemplation
of the heavenly wonders.
The planetary tables, published at last
at Ulm in 1629 under the title of Tabulae Rudolphinae (in honor of
his first patron), represented the last great achievement of Kepler's life.
He took to the road again in the fall of 1630 to attempt to obtain the
salary and arrears due him as Imperial Mathematician from the Reichstag,
then meeting in Regensburg. Nearing 60, Kepler made the long journey from
Silesia to Bavaria on horseback. This last trip of a world-famed astronomer,
riding across half of Germany on a worn-out nag, seeking a salary earned
many years before, is one of unique pathos. The exertions of the trip brought
Kepler to Regensburg a sick man; he died there on Nov. 15, 1630. Kepler
was buried in the cemetery of St. Peter's, outside the town walls. Three
years later the cemetery was laid waste during the conquest of the city
by Duke Bernhard of Weimar, and the site of Kepler's grave is today unknown.
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Leavitt, Henrietta Swan (1868-1921),
American astronomer whose fundamental discovery of the relation between
the absolute magnitudes of Cepheid variable stars and the periods of their
light-variations provided a method for sounding the depths of space. She
is also credited with the discovery of a number of asteroids, four novas
and 2,400 variable stars.
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Lemaître, Georges Édouard
(1894-1966), Belgian astrophysicist and cosmogonist, applied the
theory of relativity to the formation of the universe. He originated the
evolutionary hypothesis, which likens the formation to the disintegration
of a radioactive atom and envisions the source of all matter and energy
in the universe as a single gigantic kernel or "primeval atom."
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Leverrier, Urbain Jean Joseph (1811-1877),
French astronomer and mathematician who was a co-discoverer (with John
Couch Adams in England) of the planet Neptune in 1846.
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Lubbock, Sir John William (1803-1865),
English astronomer and mathematician who in 1829 discovered a method for
determining cometary orbits. He later introduced uniformity into the calculations
of the deviations in lunar and planetary motion by employing time as an
independent variable.
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Moulton, Forest Ray (1872-1952),
American mathematical astronomer who developed the planetesimal hypothesis
of the origin of the solar system, which replaced Laplace's nebular hypothesis.
Moulton's research dealt with several subjects, including the motions and
stability of satellite systems, the determination of planet and comet orbits,
and the tidal theory of the earth-moon system.
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Newcomb, Simon (1835-1909),
American astronomer, proposed a unified system of astronomical constants
in collaboration with A. M. W. Downing that in 1901 became the standard
for all ephemerides. He also computed extremely accurate tables for the
motions of the sun, Mercury, Venus, Mars, Uranus, and Neptune and, in collaboration
with Albert Abraham Michelson, performed experiments to determine the speed
of light.
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Newton, Sir Isaac (1642-1727),
English physicist, mathematician, and natural philosopher. By his formulation
of the laws of universal gravitation, the establishment of the fundamental
features of physical optics, and the invention of the calculus, he reorganized
the study of physical phenomena. His Philosophiae naturalis principia mathematica
(Mathematical Principles of Natural Philosophy ), Opticks, and De analysi
are considered among the greatest scientific works ever produced by human
intellect. Newton's brilliant and revolutionary contributions to science
explained the working of a large part of inanimate nature in mathematical
terms and suggested that the remainder might be understood in a similar
fashion. By taking known facts, forming a theory which explained them in
mathematical terms, deducing consequences from the theory, and comparing
the results with observed and experimental facts, he united, for the first
time, the explanation of physical phenomena with the means of prediction.
By beginning with the physical axioms of the laws of motion and gravitation,
he converted physics from a mere science of explanation into a general
mathematical system. From the confusion of the accepted theories of light
and color, his experiments explained the phenomena of color and anticipated
modern developments in light theory. His invention of calculus gave science
one of its most versatile and powerful tools.
To him, in the words of Albert Einstein,
"nature was an open book whose letters he could read without effort. The
conceptions which he used to reduce the material of experience to order
seemed to flow spontaneously from experience itself, from the beautiful
experiments which he ranged in order like playthings and describes with
an affectionate wealth of detail. In one person he combined the experimenter,
the theorist, the mechanic and, not least, the artist in exposition. He
stands before us, strong, certain and alone."
Newton was born on December 25, 1642 --
the year Galileo died -- in Woolsthorpe, Lincolnshire; he was a boy of
18 when Charles II came to the throne. Newton's father died before his
birth. When he was a little more than two years old, his mother remarried,
and his upbringing was taken over by his maternal grandmother. He began
his schooling in neighboring hamlets, and, at ten, was sent to the grammar
school at Grantham, the nearest town of any size. He boarded during terms
at the house of an apothecary named Clark, from whom he may have derived
his lifelong interest in chemical operations. The young Newton seems to
have been a quiet, not particularly bookish, lad, but very ready
with his hands; he made sun dials, model windmills, a water clock, a mechanical
carriage, and flew kites with lanterns attached to their tails. He was,
however, according to a statement made late in his life, very inattentive
at school.
In 1656, Newton's mother, on the death of
her second husband, returned to Woolsthorpe and took her son out of school
with the idea of making him a farmer. He showed no talent for it, however;
the story is told about his being found under a hedge deep in study when
he should have been in the market at Grantham. His mother, after considerable
persuasion by his teacher at Grantham, who had recognized his intellectual
gifts, allowed him to prepare for entrance to Cambridge University. In
June 1661, he was admitted as a subsizar (a student required to perform
various domestic services) at Trinity College. His early notebooks show
that his studies included arithmetic, geometry, trigonometry, and, later,
Copernican astronomy and optics. He undoubtedly derived much stimulus from
the distinguished mathematician and theologian Isaac Barrow, Lucasian Professor
of Mathematics, who recognized Newton's genius and did all he could to
foster it. Newton took his bachelor's degree in January 1665.
By this time, according to his own account,
Newton had already made great progress in his "method of fluxions" (the
infinitesimal calculus). An outbreak of plague at the time caused a general
exodus from the university, and Newton returned to Woolsthorpe, where he
remained for nearly two years. It was during this time that he recorded
his first thoughts on gravitation, to which he is said to have been led
by observing the fall of an apple in an orchard. According to a report
of a conversation with Newton in his old age, he said he was trying at
that time to determine what type of force could hold the moon in its path.
The fall of the apple led him to think that it might be the same gravitational
force, suitably diminished by distance, that had acted on the apple. He
verified his conjecture approximately by a numerical calculation which
assumed the inverse square law of attraction -- a force related to the
inverse square of the distance between the sun and the planets. He did
not, at the time, pursue the matter, because the problem of calculating
the combined attraction of the whole earth on a small body near its surface
was obviously one of great difficulty.
It was during this period that he began
to investigate the nature of light. White light, according to the view
of his time, was homogeneous. His first experiments with a prism provided
the true explanation of color. Passing a beam of sunlight through a prism,
he observed that the beam spread out into a colored band of light (spectrum).
While others had undoubtedly performed similar experiments, it was Newton
who showed that the differences in color were caused by differing degrees
of refrangibility. A ray of violet light, for example, when passed through
a refracting medium, was refracted through a greater angle than a ray of
red light. His conclusions, checked by ingenious experiments, were that
sunlight was a combination of all the colors and that the colors themselves
were monochromatic -- or, in Newton's term, "homogeneal" -- and separated
merely because they were of differing refrangibility. It was also this
period, when he was about twenty-four years of age, of which he later wrote:
"At this time I was in the prime of my age for invention, and minded mathematics
and philosophy more than at any time since" -- meaning by "philosophy"
what modern science calls physics.
In October 1667, soon after his return to
Cambridge, Newton was elected to a minor fellowship at Trinity College;
six months later he received a major fellowship and shortly afterward was
created master of arts. At this time he was devoting a good deal of time
to practical work in optics. His earlier experiments with the prism had
convinced him that the perfection of the telescope was limited not so much
by the difficulty of imparting a correct figure to the lenses as by the
differing refrangibility of rays of different colors, which would, he believed,
make it impossible to bring a beam of white light to a single focus. This
chromatic aberration is caused by differences in the degree to which light
rays of different colors, and hence of different wavelengths, are bent
in passing through the lens. Achromatic lenses, those in which chromatic
aberration is corrected by compounding units of glasses differing in their
index of refraction, and which Newton was unable to envision, are the modern
solution to the problem.
He then turned his attention to reflecting
telescopes as the only practicable solution. A design for a reflecting
telescope had been put forward in 1663 by the Scottish mathematician James
Gregory, but Newton was the first to construct such an instrument (1668).
It magnified about forty diameters, although its length was only six inches
(15 cm) and differed slightly from Gregory's in design. Chemical or alchemical
and metallurgical studies also engaged Newton's attention at this time,
as they seem to have done intermittently throughout his scientific life.
In 1669 Newton gave Barrow an important
manuscript, usually known by its shortened Latin title, De analysi, which
contained many of his conclusions on the calculus, and through him these
results were made known to several of the leading mathematicians of Great
Britain and Europe. The paper was, however, not printed until 1711. Toward
the end of 1660 Barrow resigned his chair, and through his influence Newton
was appointed to succeed him. He chose optics as the subject of his first
course of lectures.
In 1671 the Royal Society invited Newton
to submit his telescope for inspection. He sent one similar to that already
mentioned. The Society established Newton's priority by publishing a description
of the instrument. Early in the following year he was elected a Fellow
of the Royal Society, and shortly afterward offered to submit an account
of his discovery of the composite nature of white light, which he describes
as "....the oddest if not the most considerable detection which hath
hitherto been made in the operations of nature." Much impressed by his
account, the Society had it printed. This publication elicited a long series
of objections to Newton's views -- many of them ill-founded -- coming chiefly
from the Continent but also from the erratic genius, Robert Hooke, who
was curator of the Royal Society. Newton answered these objections carefully
and at first patiently, but later with growing exasperation. By 1675 he
wrote to the secretary of the Society, "I see I have made myself a slave
to philosophy, but if I get free of Mr. Linus' business (Linus was one
of the most troublesome of the objectors) I will resolutely bid adieu to
it eternally, excepting what I do for my private satisfaction or leave
to come out after me. For I see a man must either resolve to put out nothing
new, or to become a slave to defend it." These controversies augmented
the secretiveness and intolerance of contradiction which marked Newton's
character in his later life.
In the ensuing years Newton was occupied
with various mathematical, optical, and chemical investigations, and by
1679 he was again working on the problem of planetary orbits. The idea
of an attraction according to the inverse square of the distance between
the sun and the planets -- which he had assumed in his tentative
calculations at Woolsthorpe -- was now being widely discussed. This law
of attraction follows, in the simple case of a circular orbit, from Johannes
Kepler's Third Law relating the times of revolution of the planets around
the sun to the sizes of their orbits together with the expression for the
centripetal acceleration of a body moving in a circle given by Christiaan
Huygens in 1673. The inverse problem of determining the orbit from the
law of force, which had been the subject of discussion between Hooke, Wren,
and Edmond Halley, had baffled everyone before Newton, who solved it about
1680. It was probably soon after this that he found the missing link in
the identification of the force between bodies of the solar system with
the force of terrestrial gravity, namely the theorem that a spherically
symmetrical distribution of matter exerts the same attraction at external
points as if its mass were concentrated at its center.
In August 1684 Halley visited Cambridge
to consult Newton on the problem of orbits. During a discussion with Halley
regarding the shape of the orbit under the inverse square law of attraction
toward a fixed center, Newton suggested that it would be an ellipse. Unable
to find the calculation from which he had derived the answer, Newton promised
to send it to Halley, which he did a few months later. On a second visit
Halley was shown "a curious treatise de motu" (on motion) of twenty-four
pages, which at Halley's request was registered with the Royal Society
in February 1685. This tract on the laws of motion formed the basis of
the first book of Philosophiae naturalis principia mathematica, the treatise
which has been the chief vehicle of Newton's influence on the scientific
thought of succeeding generations. This work is by common consent one of
the most important books ever written; its composition in the space of
about eighteen months was an intellectual feat unsurpassed before or since.
Halley's part in the development of the Principia was highly significant.
He tactfully smoothed over differences between Newton and Hooke, who claimed
that he had communicated the law of the inverse square to Newton. In a
fit of pique, Newton decided to suppress the third book of his work, that
dealing with dynamical astronomy, but Halley succeeded in averting this.
It was Halley, too, who saw the work through publication and undertook
the cost of printing. The Principia finally appeared about midsummer 1687
and was immediately hailed as a masterpiece, although Newton had intentionally
made the book difficult "to avoid being baited by little smatterers in
mathematics." What captured the imagination of the scientific community
was the grand unifying idea of gravitation, with effects extending throughout
the solar system, and explaining by one principle such diverse phenomena
as the tides, the precession of the equinoxes, and the irregularities of
the moon's motion.
In spite of this favorable reception, it
was not until some fifty years later that the Newtonian scheme finally
supplanted René Descartes' more qualitative and graphic vortex theory
among scientists and in university teaching. When it first appeared, Newton's
work was regarded as affording incontrovertible evidence of design in the
universe, pointing to a God who is the author and creator of all things.
That Newton himself regarded his work in this light is clear from what
he says in the General Scholium at the end of the Principia (second
edition): "This most beautiful system of the Sun, Planets and Comets could
only proceed from the counsel and dominion of an intelligent and powerful
being, a God in fact, to discourse of whom from the appearances of things
done certainly belong to natural philosophy." It was not until considerably
later that the idea of inexorable universal law was appended to a materialist
or agnostic philosophy, not only in physics but in biology and the social
sciences as well.
A few months before publication of the Principia,
Newton came into prominence as a defender of academic freedom. King James
II, who hoped to reestablish Roman Catholicism, had issued a mandate in
February 1687 calling on Cambridge to admit a certain Benedictine monk,
Alban Francis, to the degree of M.A. without requiring him to take the
usual oaths of allegiance and supremacy. The university was obdurate in
its refusal. Newton took a prominent part in defending its position. The
senate appointed a deputation including Newton, which appeared before the
commission at Westminster and successfully defended the university's rights.
After the downfall of James II, Newton was elected a representative of
the university in the Convention Parliament, in which he sat from January
1689 until its dissolution a year later. While he does not appear to have
taken part in debate, he continued to be zealous in upholding the privileges
of the university. His public duties brought a change in his retiring mode
of life and required frequent journeys to London, where he met many prominent
persons, including the philosopher John Locke, and the diarist Samuel Pepys.
Possibly as a reaction to the intellectual effort of writing the Principia,
Newton about this time suffered a period of depression amounting to a nervous
breakdown. He wrote that he was the victim of "a distemper which this summer
has been epidemical," probably some severe form of influenza. Opinions
differ among Newton's biographers as to the permanence of the effects of
the attack. It is a fact, however, that immediately after this illness
he was able to attack the intricate problem of the moon's motion, which
-- he wrote -- kept him awake and made his head ache. This work involved
a correspondence with John Flamsteed, the first Astronomer Royal, on whose
lunar observations he depended. Their relationship was marred by misunderstandings
and quarrels and ended in complete estrangement. In 1698 Newton tried to
carry his lunar work further and resumed collaboration with Flamsteed,
but difficulties again arose and Flamsteed was accused of withholding his
observations. The quarrel had not been reconciled when Flamsteed died in
1719.
In 1696, through the efforts of Newton's friends to find
some remunerative public post for him, he was appointed warden of the mint.
This necessitated his living in London, where he resided until his death.
Newton's work at the mint included a complete reform of the coinage, which
had become debased through the fraudulent practice of clipping the edges
of coins. The reform involved minting of coins of standard weight and composition
and having milled edges. This task, which called for great technical and
administrative skill, was successfully carried out in the three years up
to November 1699, when Newton was promoted to the mastership of the mint,
a well-paid post which he held for the remainder of his life.
In 1701 Newton resigned his chair and fellowship
at Cambridge, and in 1703 was elected president of the Royal Society, an
office to which he was reelected annually thereafter. In 1704, a year after
the death of his great rival, Hooke, he brought out his second great treatise,
the Opticks. This was written in English, but later had a Latin translation.
Most of the work on the Opticks was done before he went to live in London.
One of its most interesting features is a series of general speculations
appended to the second edition (1717) in the form of "Queries," which bear
witness to his profound insight into physics. Many of his surmises foreshadow
modern developments, but it is necessary to guard against reading too much
into Newton's words.
In 1705 Newton was knighted by Queen Anne; he was by
now the acknowledged dean of British, and indeed European, scientists.
Among his activities in the last two decades of his life was the preparation
of the second and third editions of the Principia (1713, 1726). Second
and third editions of the Opticks were also published (1717, 1721). A constant
preoccupation during these years was the protracted controversy with Gottfried
Wilhelm von Leibniz into which Newton had been drawn and which continued
even after Leibniz' death, over the question of priority in the invention
of calculus. This controversy embittered Newton's closing years, clouded
scientific relations between Great Britain and the Continent, and seriously
retarded the progress of mathematical science in Britain. It is now generally
agreed that Newton was the first to unify and make explicit what had been
latent in the work of his various forerunners, such as Francesco B. Cavalieri,
Pierre Fermat, and Descartes. Although he himself was able to solve many
physical problems by means of his differentials, his approach and particularly
his notation were not adapted to general use. Liebniz' discoveries were
later in time, though independent; however, he preceded Newton in publishing
a full account, and he introduced a notation which has survived with few
changes. Newton's reluctance to publish his discoveries at the time he
made them was undoubtedly a contributory cause of the dispute.
Newton's fame rests securely on his application
of the mathematical method of the study of nature, and his having been
first to bring under one general principle -- the law of gravitation --
a wide range of natural phenomena. He consolidated the foundations of dynamics
as the true basis of a mechanical picture of the universe and made applications,
chiefly to celestial phenomena, undreamed of before his time. His achievements
in the use of infinite series and in differential and integral calculus
went so far beyond what had been done before that he is often regarded
as the chief discoverer in these fields.
It would be difficult to exaggerate the influence Newton's
work has had on the development of physical science. During the two centuries
following publication of the Principia, there was a great expansion in
the range of phenomena that yielded to treatment by the mathematical and
dynamic methods initiated by him. Much of this expansion can be described
as a sequel to the Principia. It was not until early in the twentieth century
that the foundations on which Newton's work rests were seen to be in need
of drastic revision, a revision which has led to the modern theory of relativity
and to the quantum theory. But for systems of ordinary dimensions, involving
velocities which do not approach the speed of light, the dynamic principles
formulated by Newton nearly three centuries ago are still valid.
Besides his scientific work Newton left
voluminous writings on theology, chronology, alchemy, and chemistry, in
all of which he was profoundly learned.
In 1725 Newton moved from London to Kensington
-- then a village -- for reasons of health. He died there on Mar. 20, 1727.
He was buried in Westminster Abbey, the first scientist to be so honored.
Further Reading on Isaac Newton
A modern assessment of Newton and his work, on both a
popular and scholarly level, will be found in the following texts: Newton,
His Friends and His Foes by A. Rupert Hall (Ashgate, 1993); Newton: Texts,
Backgrounds, Commentaries by I. Bernard Cohen & Richard S. Westphal
(Norton, 1993); Newton's Laws of Motion by School Mathematics staff (Cambridge
University Press, 1993); Newton's Scientific and Philosophical Legacy edited
by P. B. Scheurer and G. Debrock (Kluwer, 1988); Newton and the Scientific
Revolution by Richard S. Westphal (Indiana University Lilly Library, 1987);
In the Presence of the Creator: Isaac Newton and His Times by G. E. Christianson
(Free Press, 1984); Never at Rest: A Biography of Isaac Newton by Richard
S. Westphal (Cambridge University Press, 1981); and Newton on Matter and
Activity by Ernan McMullin (University of Notre Dame Press, 1979).
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Olbers, Heinrich Wilhelm Matthias (1758-1840),
German astronomer and physician, the inventor of a method of orbit calculation
still in use. He also set forth the belief that asteroids originated from
an exploded planet and is credited with the discovery of the second and
fourth asteroids (Pallas and Vesta, respectively).
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Pickering, William Henry (1858-1938),
American astronomer, was born at Boston, Feb. 15, 1858. He graduated from
the Massachusetts Institute of Technology in 1879 and taught there from
1880 to 1887. In 1887 he became professor of astronomy at Harvard, and
was interested in astrophotography. He found photographically that the
entire constellation of Orion is immersed in nebulosity. In 1891 he and
his brother, Edward Charles Pickering, together established a southern
Harvard station at Arequipa, Peru. He and Andrew E. Douglass proved the
dark areas of Mars were not seas.
In 1893 Dr. Percival Lowell commissioned Pickering and
Douglass to establish the Lowell Observatory at Flagstaff, Arizona. Pickering
returned to Harvard and discovered Saturn's ninth satellite. He established
another Harvard station at Mandeville, Jamaica, and made extensive lunar
surveys. His work, The Moon , was published in 1903. Later he announced
changes observed on the moon. Pickering also did original research on meteors
and novae. He made a major contribution on trans-Neptunian planets, reaching
conclusions essentially similar to John Lowell's; and Pluto was later found
nearer Pickering's predicted position. He also believed in other trans-Neptunian
planets. Pickering was one of the world's leading observers, the planets
being his main interest. Under his direction many reports on Mars were
made, and he was a prolific writer of astronomical papers. He died Jan.
16, 1938.
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Ptolemy (Claudius Ptolemaeus)
(fl. second century a.d.), the most famous
astronomer and geographer of the ancient world, whose theories placed the
earth at the center of the universe. His nationality, birthplace, and dates
of birth and death are unknown. Ptolemy himself recorded having made astronomical
observations at or near Alexandria, and two of his observations are dated
a.d. 127 and 151. His star catalogue, part of his work on astronomy, the
Almagest, belongs to a.d. 137. Other information about Ptolemy's life comes
from very late sources and is of doubtful reliability. He is said to have
been alive during the reign of Marcus Aurelius (a.d. 161-180) and to have
died at the age of seventy-eight. It may be assumed that he was born around
the end of the first century. Ptolemy's two most important works, the Almagest
and the Geography, brought to a culmination ancient scientific investigations
in the fields of astronomy and geography. So seemingly perfect were his
masterworks that they dominated scientific research for 1,400 years. Virtually
no improvements were made upon the Geography during that time, and advances
by Arab astronomers consisted essentially of refinements of the Almagest.
Although Ptolemy was the most celebrated ancient authority, he was not
the most gifted or creative mathematician, astronomer, or geographer. His
genius lay rather in his extraordinary ability to assemble the research
data of his predecesssors, to introduce improvements of his own, and to
present the results as a logical and complete system, written in a readily
intelligible form. His very mastery of the art of compiling the equivalent
of textbooks or handbooks on scientific subjects helped retain the level
of knowledge in these subjects to the limitations of Ptolemy and his times.
The modern scientific age may be said to have begun in these fields when
the authority of Ptolemy's two works was overthrown.
The Almagest
The Almagest is Ptolemy's greatest work, the title being
a combination of the Arabic definite article and of the Greek word megiste,
meaning "greatest." Ptolemy's original title, Mathematike Syntaxis
("Mathematical System"), indicates the theoretical character of his book.
The work stands at the apex of centuries of effort on the part of Greek
astronomers to explain the peculiar behavior of celestial bodies. It consists
of thirteen books and purports to be a complete handbook of the heavens.
(For an account of prior developments in Greek astronomy, see Astronomy.)
Books I and II of the Almagest are introductory,
setting forth Ptolemy's basic astronomical assumptions and his mathematical
methods. He presents his proofs that the heavens and the earth are spheres
and that the earth is at the exact center of the universe. He assumes that
the earth is stationary and that the heavens make a daily rotation on a
celestial axis. Book I contains his Table of Chords for arcs subtending
angles from ¹° to 180° by steps of ¹°. This is the
equivalent of a table of sines of half the angles respectively. Its construction
was derived from a lost work of the Greek astronomer Hipparchus (c. 190
b.c.-c. 125 b.c.) and became the basis for later developments in
trigonometry. Book II contains such matters of mathematical geography as
the determination of the longest day of the year in a place of a given
latitude and the location of latitudes ("climates") in the inhabited zone,
according to the length of the longest day in each latitude.
Books III and IV deal with the motions of
the sun and moon. Ptolemy adopts Hipparchus' theory to explain the anomaly
of solar motion (actually the elliptical orbit of the earth about the sun),
using a hypothesis based on epicycles and eccentrics. Ptolemy's lunar theory
is much more complicated. He supposes that the moon moves on an epicycle
whose center moves from west to east on an eccentric deferent. The center
of the deferent, in turn, revolves from east to west about the earth, the
entire scheme lying in the plane of the moon's apparent motion. To an observer
on earth, the opposite motions of the center of the epicycle and of the
deferent are equal relative to the line joining earth and sun. Thus the
epicycle is at apogee on the eccentric at the time of the new and full
moon and at perigee at the time of half moon. The resulting scheme was
satisfactory in overcoming the major defect in Hipparchus' lunar theory
and in accounting for the periodic fluctuations, known as evection, for
which Ptolemy obtained a nearly true value.
Book V deals with various subjects: a continuation
of the lunar theory; the construction of an astrolabe; estimates of the
diameters of the sun, moon, and earth's shadow; and estimates of the dimensions
of sun, moon, and earth, and of the distance of the sun. Book VI deals
with solar and lunar eclipses. Books VII and VIII are on the fixed stars,
arranged according to their constellations. The latitude and longitude
of each star are given in degrees and minutes, and the magnitude is given
in a range from 1 to 6. It is not clear how much of this catalogue represents
independent observations by Ptolemy and how much was derived from Hipparchus'
catalogue with allowances for precession during the three intervening centuries.
Ptolemy also discusses here the precession of the equinoxes, the Milky
Way, and the construction of a celestial globe.
Books IX to XIII deal with planetary motions,
a subject not disposed of by Hipparchus. Book IX deals with the order of
the planets (their relative distances from the earth) and their periods
of revolution, and then takes up the theory of Mercury's motion. Book X
deals with Venus and Mars and XI with Jupiter and Saturn. Book XII discusses
stations and retrogradations of each of the planets and the maximum elongations
of Mercury and Venus. Ptolemy's basic scheme represents Venus and the three
superior planets as moving from west to east on epicycles whose centers
move in the same direction on eccentric deferents. The center of the epicycle
is supposed not to move with uniform angular velocity about the center
of its deferent, but about a point lying on a line projected from the earth
through the center of the deferent at twice the distance between the earth
and the center of the deferent. Deferents and epicycles are represented
as being inclined to the ecliptic at various angles. The scheme for Mercury's
motions is much more complicated. (See Astronomy,
History of.)
The Geography
Ptolemy's Geography held the same position
in its field that the Almagest held in the field of astronomy. It was regarded
as a complete and virtually infallible treatment of the subject and dominated
the theory of geography until the Renaissance. It should be noted that
the Almagest is distinctly superior to the Geography as a scientific treatise.
The Almagest, while defective astronomically, has validity as a mathematical
work. The Geography, on the other hand, combines advances in theory with
serious limitations in application. Ptolemy introduces his subject with
a clear exposition of the principles of cartography -- the methods of determining
the latitude and longitude of places by astronomical means and of representing
a spherical surface on a plane -- and then proceeds to base the body of
his geographical treatise on rough data accumulated mainly from the dead
reckoning of travelers on land and sea. Because Ptolemy's introduction
of his subject is mathematical and the body of his work consists of an
impressive list of more than 8,000 place names -- cities, islands, mountains,
river mouths, etc. -- it was erroneously assumed that the entire work was
scientific. On the contrary, although his presentation of the theoretical
aspects of cartography would satisfy the requirements of an elementary
textbook today, it may be assumed that he was fully aware that the exact
location of places had not been accurately determined in his day.
In Book I of the Geography, Ptolemy discusses
the reliability of determining relative positions on the earth's surface
by astronomical means and by measurements of distances made over land or
estimates of distances of voyages. He admits that astronomical observations
are more reliable, but points out that for much of the surface of the known
world no data exist other than the dead reckoning of travelers. He feels
the safest practice is to use terrestrial and astronomical data to check
each other. He then offers explicit instructions for constructing a world
map on a sphere (much like present-day commercial globes) or on a conical
projection or a modified spherical projection laid on plane surfaces. The
remaining seven books are devoted almost entirely to the list of place
names with their geographical coordinates.
Since the bulk of Ptolemy's data was obtained
from travel sources -- much of it compiled by his immediate predecessor,
Marinus of Tyre (c. a.d. 120) -- Ptolemy's atlas contains many errors,
gross and small. Eratosthenes' nearly correct figure for the earth's circumference
had been reduced by more than one-fourth by Posidonius, and Ptolemy adopted
the smaller figure. Ptolemy placed the zero meridian at the Canary Islands
and, following travelers' exaggerated estimates of distances across Asia,
supposed that the known world extended over 180° (actually 130°).
On the 180th meridian of his map, China is a great land mass stretching
from the top of the map to the equator, and it was natural to assume that
the unknown part of the Asian continent extended much beyond into what
is now the Pacific Ocean. It was Ptolemy's classical conception of the
world -- a sphere reduced by one-fourth from actual size, with a land mass
extending over perhaps two-thirds of the northern hemisphere -- that gave
Columbus the confidence to attempt a westward sailing to India. Ptolemy
appended to his work an atlas of 27 maps -- ten regional maps of Europe,
four of Africa, 12 of Asia, and a map of the known world. So impressive
was his work that for more than a century after the voyages of Columbus
and Magellan had disproved his basic conceptions, maps continued to appear
in the Ptolemaic style. Some of his erroneous conceptions persisted on
maps in the 17th and 18th centuries and, for the interior of Africa, into
the 19th century.
Other Works
Ptolemy's versatility and his genius for
expository writing are evident in other important treatises which he wrote
on optics and music. The work on optics survives only in a Latin version
of a lost Arabic version of the lost original Greek treatise. It was in
five books, of which Book I and the end of Book V are missing. Books III
and IV are on catoptrics. Ptolemy uses measurements to prove that the angle
of incidence is equal to the angle of reflection. Book V deals with refraction.
He introduces experiments in re fraction through water and glass
at different angles of incidence and then undertakes to apply his results
to astronomy, in the determination of the degree of refraction of starlight
on penetrating the earth's atmosphere. Ptolemy's treatise is the most complete
work on mirrors and optics to survive from antiquity. Ptolemy's Harmonics
has been called "the most scientific and best arranged treatise on the
theory of musical scales that we possess in Greek." After Aristoxenus'
work, it is the most important treatise on ancient music. Compared with
Aristoxenus' treatment of the subject, Ptolemy's treatise may be called
practical.
Ptolemy also wrote an elaborate work on
astrology in four books, entitled Tetrabiblon or Quadripartitum, handled
in straightforward textbook style. That he took the pains to write a lengthy
work on that pseudoscience is indicative of the spell that astrology cast
upon the ancient world.
Influence Of Ptolemaic Theory
Though the results of Ptolemy's investigations
dominated scientific research for some 1,400 years, their influence on
social, political, moral, and theological theories was perpetuated even
longer, until the period of revolution in the 18th century. Ptolemy's assumptions
of a man-centered earth in a geocentric universe were widely disseminated,
largely through medieval encyclopedias. The reconciliation of Christian
doctrine and classical lore by Albertus Magnus (c.1193-1280) and Thomas
Aquinas (1225-1274) made the beliefs of antiquity both acceptable and useful
to the Middle Ages and the Renaissance.
The study of the universe led to a reexamination of humanity
in relation to its surroundings, and Ptolemy's systematic ordering of the
planets, together with his suggestion that each planet affected certain
classes of people, was interpreted by the Church as a part of a great hierarchy
or chain of being, with God and the angels as the highest link, then man,
woman, animals, plants, and stones as the lower links of the chain. Such
lore, accepted by the Church and combined with the account in Genesis of
the creation of the world in six days, provided the background of writers
of both prose and poetry from the Middle Ages to the 18th century. The
great chain of being was assumed to be divinely ordered, in a society of
the three feudal estates -- nobility, clergy, and commons -- each responsible
to the body politic for its peculiar function or duty. So firmly were such
concepts still held in 1616 that Galileo, who asserted the Copernican theory
of a sun-centered universe, was summoned before the Inquisitors of Rome
and forced to recant.
Evidences of the influences of Ptolemy in
literature are innumerable. Some writers mention him explicitly as their
authority. Others, such as Dante and Milton, make the Ptolemaic universe
the basis for the entire organization of their works. The wife of Bath
in Chaucer's Canterbury Tales refers to "Ptholomee; Rede in his Almageste"
and to "The wise astrologien Daun Ptholome, That seith this proverb in
his Almageste." The clerk Nicholas in The Miller's Tale kept "his
Almageste, and bookes grete and smale" at his bed's head. In The Man of
Law's Tale Chaucer interpolated a passage from Ptolemy on the influence
of the primum mobile (the outermost sphere) and wrote "Ptholomeus, lib.
I, cap. 8" in the margin.
The notion of cosmic order pervades all
of Spenser's work, as in Colin Clouts Come Home Again and throughout
The Faerie Queene , where all the creatures are "rankt in comely row."
Such Elizabethan prose authors as Sir Thomas Elyot, Sir Walter Raleigh,
and Richard Hooker tell of the necessity for order and degrees in the chain
of being or of the influence of the stars on life, as instruments of Divine
Providence. Henry Peacham's Compleat Gentleman (1622) cites the Geography
of "Ptolemy and others" as a study necessary for a gentleman and summarizes
Ptolemy's order of planets.
The "star-crossed lovers" of Romeo and Juliet
, Sir Toby's confused astronomy in Twelfth Night , the description of the
music of the spheres in the Merchant of Venice , and Horatio's description
in Hamlet of "stars with trains of fire," eclipses of the sun, and other
omens of "heaven and earth" as precursors of disaster are familiar evidences
of Shakespeare's Ptolemaism. Hamlet, too, recognizes man's position in
the chain of being in finding man "how like an angel" and "the paragon
of animals." The most complete single statement of the doctrine of Ptolemaism
is found in Ulysses' speech in Troilus and Cressida , with its threat of
chaos when the chain of being is broken or degrees are destroyed: "Take
but degree away, untune that string, And hark what discord follows!" Here
the heavens, the earth, and man are all included; the chain is complete
except for God and the angels and animals, vegetables, and minerals. The
sun maintains order in the macrocosm as the king maintains it in human
relations.
John Milton's Paradise Lost (1667) includes
a dialogue on astronomy in which Adam and the angel Raphael compare the
Ptolemaic and Copernican theories, but elsewhere Milton adheres to Ptolemaic
concepts. In Paradise Lost Satan's journey to earth takes him past
"the planets seven, and....the fixt, And that Crystalline Sphere."
The great chain of being is described by the angel Raphael, and man's position
as center of the universe is reasserted.
The doctrine persisted until the 18th century,
when Pope, in his Essay on Man (1733), could still acclaim the "Vast chain
of being!" (Epistle I, II, 237-256), so essential to the universe, lest
"Planets and suns run lawless through the sky" and man be "in endless error
hurled."
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Roemer, Olaus (1644-1710),
Danish astronomer, born at Aarhaus, Jutland, Sept. 21, 1644. After studying
at the University of Copenhagen, he spent nine years at the Royal Observatory,
Paris, then directed by J. D. Cassini. He discovered that the eclipses
of Jupiter's satellites seemed to take place at different times, depending
on the time of year at which observations were made. He concluded that
this discrepancy arose from the difference in the distance that the light
from Jupiter had to travel when the earth was nearest to Jupiter and when
it was farthest from it, six months later. He found "a retardation of light
of twenty-two minutes, for an interval of space double the sun's distance
from the earth." This first announcement of the discovery of the finite
velocity of light probably ranks second (the law of gravity first) among
man's greatest achievements. Roemer's inventions and discoveries were almost
unparalleled: he invented the transit instrument, the altazimuth, the equatorial
telescope, and other equipment. In 1681 Roemer was recalled to the University
of Copenhagen as royal professor of mathematics and astronomy. He invented
the transit and altazimuth and set up these instruments along with a form
of equatorial telescope at his observatory on the outskirts of Copenhagen.
A great fire in 1728 destroyed most of his records, yet his improved observation
technic and inventions advanced astronomy immensely. Roemer died in Copenhagen,
Sept. 23, 1710.
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Russell, Henry Norris (1877-1957),
American astronomer, was born at Oyster Bay, N.Y., Oct. 25, 1877. He studied
under Charles A. Young at Princeton University and under Sir Robert Ball
at Cambridge University. In 1905 he succeeded Young at Princeton as professor
of astronomy and director of the observatory. Russell made fundamental
contributions in cosmogony and stellar evolution. With Hertzsprung he discovered
that stars compose two great classes -- dwarfs and giants. The giant stars
represent changes in heating up, and the dwarf stars show changes in cooling.
His theory of stellar evolution was criticized by Sir Arthur Eddington,
and in 1925 the theory was revised; Russell's modifications have since
been upheld. In 1947 he was made research associate at the Harvard Observatory.
Russell died on Feb. 18, 1957, in Princeton, N.J.
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Schmidt, Bernhard Voldemar (1879-1935),
German optical instrument maker, introduced the use of a specially designed
plate in astronomical telescopes to eliminate spherical aberration. The
resulting device, called a Schmidt telescope, can be used to photograph
wide angular fields, although a curved photographic plate must be employed.
Despite the loss of his right hand in a childhood accident, Schmidt was
the foremost grinder of astronomical mirrors of his day.
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Schröter, Johann Hieronymus (1745-1816),
German astronomer, called the founder of selenography (the study of the
moon's surface features).
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Sitter, Willem de. (1872-1934),
Dutch astronomer and proponent of the relativity theory, was born at Sneek,
the Netherlands, on May 6, 1872. At the University of Groningen, he worked
with Jacobus C. Kapteyn, head of the astronomical laboratory. In 1897,
invited by Sir David Gill, Director of Capetown Observatory, he went to
the Cape as mathematical computer. Gill inspired him to follow the study
of Jupiter's satellites as the subject of his doctoral dissertation, an
absorbing interest to him for the rest of his life, leading to determination
of variability of the earth's rotations. De Sitter returned to Groningen
in 1900, becoming Kapteyn's assistant, and in 1908 he was appointed professor
of astronomy at the University of Leiden. In 1919, de Sitter also became
director of the observatory, which he reorganized with government instructions
and funds, making Leiden one of the leading observatories of Europe. In
1911, de Sitter published a paper on relativity, preceding by three years
that in which Einstein gave his generalized theory. In 1916 and 1917, de
Sitter presented three papers to the Royal Astronomical Society (London),
giving a complete exposition of the mathematical theory of relativity and
details of its astronomical consequences, with an attempt to calculate
the radius of the universe from observation of the mean density of matter.
The third paper set forth his most important contribution to the subject,
the hyperboloid de Sitter universe, an alternative to the right-cylindrical
Einstein universe. Einstein's papers were not available because of war
conditions, but de Sitter's interpretations influenced the form in which
the theory was presented, gaining acceptance for it by scientific men and
leading to the British eclipse expeditions of 1919. Without de Sitter's
work, Einstein's conclusions as to the amount of deviation of light passing
near the sun would have lacked the confirmation gained in observations
of the eclipse. Generous and devoted to scientific truth, de Sitter welcomed
the nonstatic theories of the universe arrived at independently by Friedmann
in 1922, and by G. E. Lemaître in 1927. With de Sitter, Lemaître
worked out the astronomical consequences in considerable detail. In 1930,
the papers announcing these discoveries came to the attention of
the astronomical world, arousing continuing discussion. In 1931, de Sitter
began a U.S. lecture tour. He spent the winter at Mount Wilson Observatory
in California, studying, with Einstein, the spiral movements of galaxies
and the expansion of the universe. In the spring of 1932, the two scientists
jointly stated that there is more evidence of the expansion of the universe
than that it is static, the great star clusters apparently rushing away
at enormous speeds. De Sitter delivered three lectures at the University
of California, which, updated before publication in 1933, gave the latest
data available on the idea of the expanding universe. On Nov. 22, 1934,
de Sitter died after a brief illness. See also Relativity.
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Struve, Otto Wilhelm von (1819-1905),
German astronomer, discovered more than 500 double stars and calculated
the constant of precession. He determined Neptune's mass, the dimensions
of Saturn's rings, and the velocity of the sun. He succeeded his father,
Friedrich Georg Wilhelm von Struve (1793-1864), as director of the Imperial
Observatory at Pulkova in 1862.
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Weizäcker, Baron Carl Friedrich
von (1912- ), German cosmogonist and physicist, proposed
the first dust-accumulation theory of planetary formation that adequately
accounted for the distances of the planets from the sun. His hypothesis,
based on the older Kant-Laplace hypothesis, freed cosmogonists from the
need to rely on stellar collision theories to explain planetary distances.
If you know of any other great astronomers please feel
free to e-mail me, and tell
me a little about them. I would be glad to add them to this list of famous
astronomers.