improvement cessors to place astronomy in the state in which Eudoxus of it stood at the birth of Newton. Considering his means, his observations are perhaps unequalled.

Calippus, B.C. 330, introduced the on the former known by his name. Cnidos, B.C. 370, brought into Greece, according to Pliny, the year of 365 days, and wrote some After the death of Hipparchus there is no works, one of which exists in the poetical version astronomer of eminence till Ptolemæus. Between of Aratus. Timochares and Aristyllus, B.C. 300 (?) them we have Hypsicles of Alexandria; Geminus made the observations which afterwards enabled (of Rhodes ?), B.C. 70; Posidonius. Theodosius Hipparchus to discover the precession. Pytheas, of Bithynia, B.C. 50, left a work on spherical geoabout the time of Alexander, measured the lati- metry, another on climates, and a third on the tude of Marseille with tolerable accuracy. The phenomena of day and night. Sosigenes of Alexwork of Aristotle on astronomy is lost; and, what andria, B.C. 50, corrected the calendar under is still more to be regretted, that of his disciple Julius Cæsar. Hyginus left an astronomical deEudemus on the history of astronomy. The scription of the heavens. Manilius, a Roman, poem on the Sphere, attributed to Empedocles, B.C. A.D. 10, wrote an astronomical and astrological 450, is probably much more modern. poem. Seneca, A.D. 50. His book on natural We pass over Autolycus, B.c. 300; Euclid of philosophy contains many pieces of information Alexandria, B.C. 300; Aratus of Cilicia, B.C. on astronomical history, but is principally remark281; Aristarchus of Samos, B.C. 280; Manetho able for his bold opinions on the nature of comets. the Egyptian, B.C. 260; and come to Eratosthenes These he declares to be planets, whose laws he of Cyrene, B.C. 240, who observed the obliquity predicted would one day be calculated, and that of the ecliptic, and the latitude of Alexandria; posterity would wonder how things so simple and from the latter, and the fact that at Syene could have so long escaped notice. Menelaus, the sun was vertical at the summer solstice, de- A.D. 80, has left three books of spherical triduced an approximation to the earth's magnitude. gonometry. Theon of Smyrna, A.D. 117? wrote His approximation makes a degree to be 700 on astronomy, and made a collection of astrostadia. His stadium is unknown. His value of nomical works. His observations are cited by the obliquity of the ecliptic-11 parts out of 166 Ptolemæus. Cleomedes wrote on astronomy. He of the whole circumference was adopted by Hip- certainly lived after Posidonius, but whether parchus and Ptolemæus. before or after Ptolemy is uncertain. He is usually considered as having lived under Augustus Cæsar.

Archimedes of Syracuse died B.C. 212. He observed solstices, and attempted to measure the sun's diameter. His writings show that trigonometry was as yet unknown.

We must suppose that there were many real observers between the epochs of Hipparchus and Ptolemæus; but from the loss of even their names, and the silence of Ptolemæus himself, it is clear that no discovery of any importance was made.

Hipparchus (of Bithynia?) B.C. 160-125, the greatest of all the Greeks in astronomy. In his youth he wrote a commentary on Aratus. He discovered the precession of the equinoxes, by Ptolemæus of Alexandria, A.D. 130-150. We comparing his own observations with those of must briefly mention his works, his system, and Aristyllus and Timochares, or others of his pre- his discoveries. The Manuarień Zúvražu, or decessors. He was the first who employed pro- Mathematical Collection,' afterwards called cesses analogous to those of plane and spherical Mıyaλn Zúvrağıs, and by the Arabs the Almatrigonometry, for which he constructed a table gest,' is the work from which we derive most of of chords. He first used right ascensions and de- our knowledge of the Greek astronomy. We clinations, which he afterwards abandoned in find there a full account of the observations and favour of latitudes and longitudes. He suggested discoveries of Hipparchus; those of Ptolemæus the method of referring terrestrial positions to himself; the reasons and elements of his system; latitude and longitude, and was probably the in- various mechanical arguments against the motion ventor of the stereographic projection. He de- of the earth, which show that the first principles termined the inean motion of the sun and of its of dynamics were utterly unknown; a description apogee, the inequality of the sun's motion, and of the heavens and the milky way, and a catathe length of the year, to greater exactness than logue of stars, which we may be nearly certain his predecessors. He found the mean motion of was that of Hipparchus, reduced to his own time the moon, of her nodes, and of her apogee; her by an assumed value for the precession, but which parallax, eccentricity, the equation of her centre, and inclination of her orbit. His observations also led him to suspect another inequality in the moon's motion, which Ptolemæus afterwards discovered (the evection.) He calculated eclipses, The Ptolemaic system was an attempt to and used the results in the improvement of the represent the motions of the planets by supposing elements. He made one of the first steps to them to move uniformly in circles, the centres wards a correct representation of phenomena, by of which circles themselves moved uniformly in supposing the sun to move round the earth in circles round the earth. The angular motions of a circle, the earth not being at the centre. His the planets, as then known, were sufficiently well catalogue of the longitudes and latitudes of 1081 represented by this system; not so their changes stars was the first at all worthy of the name. If of distance from the earth, as seen in their appaHipparchus had possessed the pendulum and the rent diameters. This was the universal system of telescope, fifty years might have enabled his suc-after-times till Copernicus.

has been asserted to have been corrected by new observations; a theory of the planetary motions; the length of the year; the instruments he em ployed, &c.

of whom we know anything between Hipparchus and Tycho Brahé.

We must also mention Alfraganus, or Al-Fergani, and Thabet ben Korrah, both about A.D. 950; Ebn Yunis, and Abul-Wefa, about A.D. 1000; Alphetragius of Morocco, A.D. 1050; Arsachel, a Spanish Moor, A.D. 1080; his contemporary, Alhazen, Geber, and Abul Hassan.

The principal discovery of Ptolemæus is that of the lunar evection, an inequality such as would be caused by an alternate increase and diminution of the eccentricity of the moon's orbit. He also discovered the refraction, and made some tolerably correct experiments to determine its law. He explained the apparent enlargement of the discs of the sun and moon when near the horizon. He extended the projection of the sphere of Hip- We have Persian tables (of the eleventh cenparchus. He entered into the investigation of tury?) translated by George Chrysococca, a Greek every point which Hipparchus had touched; in physician, in the fourteenth century; but the best some instances finding more correct values; in known are those of Nasireddin, published A.D. others, altering without amending. He was not 1270, under the protection of Hulagu, grandson an astronomer only, but wrote on geography, of Genghis Khan, and conqueror of Persia. music, chronology, mechanics, and unfortunately Uluy Beg, grandson of Timur, A.D. 1433. This on astrology.

With Ptolemæus the originality of the Greek school ends. We must come to the Arabs before we find anything worth particular notice.

prince made a large number of observations at Samarcand. His catalogue of stars of the date above mentioned, was, in its day, the most correct ever published. He also gave tables of geogra phical latitudes and longitudes.

nology.

Sextus Empiricus, A.D. 173, described and wrote against the Chaldean astrology. Censorinus, In China, Cocheou-King, A.D. 1280, patronized A.D. 238, wrote an astrological work on the day by Kublai, brother of Hulagu, and fifth successor of nativity, containing historical information with of Genghis Khan in the partial conquest which regard to astronomy. Julius Firmicus Maternus, that prince made of China, made a great number A.D. 370, wrote on astronomy. Pappus of Alex- of good observations. He introduced spherical andria, A.D. 383; Theon of Alexandria, A.D. 385, trigonometry, and rejected the ancient chrothe most celebrated commentator on Ptolemæus; Hypatia (his daughter), murdered A.D. 415, the first female on record celebrated for her scientific talents; Martianus Capella, A.D. 470; Thius of Athens, A.D. 500; Simplicius, A.D. 546; Proclus Diadochus; Isidore, archbishop of Hispalis (Seville), A.D. 636; Bede, A.D. 720; Barlaam, the monk, A.D. 1330; and Michel Psellus, A.D. 1050.

It is remarkable that, excepting his own commentators, few of the above-mentioned authors ever quote Ptolemæus. Had it not been for the Arabs, the writings of the latter must have been lost.

Since the fifteenth century, astronomy has declined throughout the East. The Chinese received many methods from the Jesuits, but to little purpose.

Among the Hindoos, there are very few who can understand the ancient writings. The Turks and Persians have little besides astrology. We now proceed with the chain of European astronomy.

Astronomy was introduced again into Europe by means of the Greek writers, mostly through translations from the Arabic. The first translation of the Almagest' was made under the auspices of the Emperor Frederic II., about A.D. 1230.

The Alexandrian school was destroyed by the Saracens under Omar, A.D. 640; and the rise of Sacrobosco (an Englishman named Holywood), astronomy among the eastern Saracens dates from A.D. 1220, wrote a work on the sphere taken the building of Bagdad by the caliph Al Mansur, from Ptolemæus, &c. It continued for a long time in the year 762. In the reign of this prince, in great repute. He also wrote on the Calendar. translations of the Greek writers were begun; We can do no more than name his contemporary and with nearly the same instruments, and the Jordanus. Alonso X., King of Castile, A.D. same theory, as Ptolemæus, a career of four cen- 1252; Roger Bacon, A.D. 1255; the Cardinal turies of observation commenced, during which Cusa, A.D. 1440; and George Purbach, A.D. many astronomical elements, and in particular 1460. the obliquity of the ecliptic, and the precession John Müller, called Regiomontanus (died A.D. of the equinoxes, were more accurately determined.

1476), made an abridgment of the 'Almagest,' published more extensive trigonometrical tables, extended various parts of trigonometry, and was an observer, though not, in this respect, superior to some of the Arabs. His almanacs were the first which were worthy of the name, and were in great repute.

In the reign of Al Mamun, son of Harun al Rashid, himself a diligent observer, great encouragement was given to astronomy. A degree of the meridian was measured, but with what accuracy cannot be known, from our ignorance of the measure employed. We may now name George of Trebizond, called Albategnius, or Al-Batani, A.D. 880, disco- Trapezuntius, who died A.D. 1486; Bianchini, vered the motion of the solar apogee, corrected A.D. 1495; Waltherus, died A.D. 1504. the value of the precession, the solar eccentricity, The following names are inserted that the and the obliquity of the ecliptic; and published reader may know to what names to refer for the tables. He is the first who made use of sines astronomy of the time immediately preceding the (instead of chords) and versed sines. He found promulgation of the system of Copernicus. Exthe length of the year more accurately. He is, cept in this point of view there is but little inbeyond all doubt, the only distinguished observer terest attached to their labours :-Riccius, A.D.

1521; Werner, died A.D. 1528; Stöffler, died about A.D. 1531; Munster, died A.D. 1552; Fracastorius, died A.D. 1543; and Fernel, who died in 1558.

his instruments could discover, thus refuting the notion that they were atmospheric bodies. He greatly improved and extended the instruments in use, as well as all the methods of observation.

Copernicus, born 1473, died 1543. He applied himself to astronomy from A.D. 1500. In Tycho Brahé did not admit the Copernican 1530, he had finished his tables of the planets, theory; but substituted for it one of his own, and his work On the Revolutions of the usually known by the name of the Tychonic Heavenly Bodies' containing an explanation of System. This consisted in supposing the sun to the Copernican System, which, it is almost un- move round the earth, but all the other planets to necessary to say, was a revival of the opinions of move round the sun, being also carried with it the Pythagorean school on the motion of the earth. round the earth. This system explains all the It was published in 1543, and its author died im- appearances as well as that of Copernicus; and mediately afterwards. Copernicus improved the we must say (though it is always usual to relunar tables, and gave, to a considerable extent, proach Tycho for refusing to admit the simple an explanation of celestial phenomena upon his system of Copernicus) that by this means the own system. His book is a mixture of his own then unanswerable arguments against the Coperoriginal and sagacious notions and of the old phi-nican system were avoided. losophy; and he was far from being able to answer the mechanical objections of his time. What might have struck so bold a thinker, had he lived to face opposition, cannot be told; but, as the history stands, we shall come to the time of Galileo before we find all objections satisfactorily answered.

From this period, at which the preservation of printed works commences, our limits will not permit our giving even the names of many astro

nomers.

We may mention, however, Reinhold, the friend of Copernicus, and advocate of his doctrines, who formed the 'Prutenic Tables;' Recorde, who wrote the first English treatise on the celestial phenomena; Nonius, inventor of an ingenious method of division of the circle, which has often caused it to be supposed that he anticipated the invention of Vernier; Mercator (Gerard), who gave the first idea of the projection known by his

name.

Up to this time, the means of observation had been undergoing gradual improvement, more by attention to the construction of the older instruments, than by the introduction of any new principle. The Copernican theory had its advocates, but was not yet adopted by many. Algebra had been introduced into most parts of Europe, but was not yet in a state to furnish much assistance in trigonometry. Logarithms were not yet invented, nor do we find the instruments fixed in the meridian, the telescope, or the pendulum clock. The first observer, who made any important additions to the phenomena of the heavens as received from the Arabs, was Tycho Brahé, to whom we now

come.

The reformation of the calendar took place in 1582, under Pope Gregory XIII.

From the time of the death of Tycho Brahé, to that of Newton, is the next great epoch in the history of astronomy.

The following are the dates of the remarkable points for which a reader is likely to consult such a work as the present.

1581, or thereabouts, Galileo remarks the isochronism of the pendulum.

1603. Bayer's maps, in which the stars are first denoted by letters.

1609. Galileo made a telescope from a general description of a magnifying instrument made by one Jansen, in Holland. Kepler publishes his work on Mars, in which he establishes, from Tycho Brahe's observations, the elliptic form of the orbit, and the proportionality of the areas to the times. These are called Kepler's first and second laws.

1610. Galileo announces the discoveries of Jupiter's satellites-of spots on the moon-of nebula-of some new appearances in Saturn, afterwards found to proceed from the ring-phases of Venus.

1611. Galileo observes the spots on the sun. 1616. Prohibition of the theory of Copernicus by the Roman court.

1618. Kepler announces his third law, that the squares of the periodic times of the planets are in proportion to the cubes of their distances from the sun.

1627. The Rudolphine Tables' published by Kepler, from the observations of Tycho Brahé.

1631. Gassendi first observed the transit of Mercury over the sun's disc-measured the diaTycho Brahé, born 1546, began to study astro-meter of Mercury, and predicted that of Venus nomy 1560; commenced his observations at with success. Vernier published his invention of Hvene, an island near Copenhagen, 1582; was the instrument which bears his name. driven from thence, 1597; died 1601. He made a catalogue of the fixed stars, more accurate than any which preceded, gave the first table of refractions, discovered the variations and annual equation of the moon, the variation of the motion of her nodes, and of the inclination of her orbit, and that of the obliquity of the ecliptic. He also ascertained that comets (those of his day, of course) were further removed from the earth than the moon; in fact, that they had no parallax which

1633. Norwood measured the meridian from York to London, and gave a more accurate value of the degree than his predecessors. Descartes produced his system of vortices. Galileo is obliged to recant his Copernican opinions by the Inquisition of Rome.

1639. Horrox and Crabtree first observed a transit of Venus over the sun's disc. The former ascertained the diameter of Venus. They were the only two who saw this particular transit.

1640. Gascoyne applied the telescope to the quadrant, and a micrometer to the telescope.

1654. Huyghens completes the discovery of Saturn's ring.

1655. Huyghens discovers Saturn's fourth satellite.

1663. Gregory makes his reflecting telescope. 1665. Cassini determines the time of rotation of Jupiter.

1666. Cassini determines the rotation of Mars, and makes a first approximation to that of Venus. Academy of Sciences founded at Paris, and observatory first thought of and commenced in the following year. Auzout applied the micrometer to the telescope without any knowledge of Gascoyne. Newton first turned his attention to gravitation.

1669. Newton made his first reflecting telescope.

done more for astronomy than the mathematical Syntaxis of Ptolemæus, had it been similarly circumstanced: that is, the work of Ptolemæus contained only a simple account of what had been done before, with no material improvements either in methods or instruments; whereas that of Flamsteed contained both, and gave a catalogue of stars such as had not been published before.

The distinct part of Newton's great discovery, which is seldom well understood by any who have not studied it, is not the notion of attraction, which had occurred to many among the ancients, and to Borelli, it is stated, and Hook among the moderns-not the law, which had been suggested by Bouillaud or Bullialdus-but the proof that the mechanical deductions from this law of attraction really do represent the celestial phenomena; a combination of improvements in mechanics and mathematics which none but the inventor of fluxions could have made, and a specimen of sagacity which it needed the author of the optics to display. Still less is it true, as many believe, that the Newtonian theory is the 1672. Cassini discovers Saturn's third satellite. Copernican, when they speak of Newton as the 1673. Huyghens publishes his Horologium establisher of the latter. After what we have Oscillatorium,' in which are found the first theo-said, it is unnecessary to discuss this further than rems on central forces and centrifugal force. to observe, that it was Galileo who destroyed the 1675. Roemer announces his discovery of the mechanical objections to the notions of Copernivelocity of light by means of Jupiter's satellites. Greenwich observatory founded.

1671. Richer, in a voyage to Cayenne, observes the shortening of the seconds' pendulum in approaching the equator. Cassini discovers Saturn's fifth satellite.

1682. Newton, who had laid aside his theory of gravitation when he found it not capable of verification by taking the best measures of the earth in use, hears of Picard's more accurate measurement, tries it, and finds a remarkable degree of nearness to the result deduced from his celebrated law.

1684. Cassini discovers Saturn's first and second satellite.

1687. Newton publishes the 'Principia.' 1689. Roemer first used the transit instrument; that is, fixed a telescope in the meridian for the purpose of observing transits.

1693. Halley discovers the acceleration of the moon's mean motion.

1705. Halley first predicted the return of a comet, viz. that of 1758.

1715. J. Cassini discovers the divisions of Saturn's ring.

1725. Flamsteed's Historia Cœlestis.' 1727. Bradley discovers aberration. Death of Newton.

We have now brought the history to a most remarkable epoch. The great comparative perfection of instruments, the invention of the telescope, of the micrometer, of the clock, of logarithms, the introduction of algebra, the invention of fluxions, and the establishment of the theory of gravitation, in England at least, were so many steps each of magnitude unequalled in former times. But the most meritorious labours are not those which make most show. It takes as much space to say that Cassini discovered a satellite of Saturn as that Flamsteed published the Historia Cœlestis;' but the first might have been left to the present day without much loss, whereas the latter was a new era in sidereal astronomy. It would have

cus, by the sound system of dynamics of which he was the inventor, and who re-enforced the notions of Copernicus by arguments of the most forcible character drawn from probability. But it was Bradley who, by his discovery of aberration, furnished the direct and unanswerable proof of the earth's motion; and it is a coincidence worth remembering, that the year of the death of Newton was that of this remarkable accession as well to physics as to practical astronomy.

The interval between the death of Newton and the present time may be divided into two parts: the first reaching to the end of the century, abounding in magnificent discoveries both of analysis and observation; the remainder more distinguished by efforts to extend, correct, and methodize the results of the first.

1731. Hadley's quadrant invented.

1732. The introduction, by Maupertuis, of the Newtonian Theory into France. Wright's Lunar Tables.

1745. Bradley discovers the nutation.

1749. Euler's and D'Alembert's researches on the precession, D'Alembert's on the nutation, Clairaut's on the motion of the Lunar Apogee. Halley's Tables.

1751. Lacaille goes to observe at the Cape of Good Hope.

1752. Lacaille measures an arc at the Cape. 1758. Dollond's achromatic object-glass. Clairaut and Lalande's researches on Halley's comet. 1761. Transit of Venus.

1763. Lacaille's catalogue of southern stars. 1765. Harrison gains the parliamentary reward for his chronometer.

1767. First Nautical Almanac.'

1769. Transit of Venus.

1774. Maskelyne's observations on local attraction at Schehallien.

Verrier.

1781. Herschel discovers the new planet now Galle, of Berlin, detected the new planet at the called Uranus. first search, September 23, 1846, within a very 1784. Laplace's researches on the stability of short distance of the place assigned for it by Le the solar system, on the relation between the longitudes of Jupiter's first three satellites, and The progress of astronomy during the last on the great inequality of Jupiter and Saturn. thirty years has consisted chiefly in the disGeneral Roy measures a base on Hounslow Heath covery of a very large number of planetoids or for the connection of the observatories of Paris small planets (these are now over 160, and and Greenwich. Herschel's catalogue of Nebulæ. there is every prospect of still further additions); 1787. Laplace's theory of Saturn's ring, and in the predicted returns of comets of short periods, explanation of the acceleration of the moon's mean and the discovery of the composition of comets motion. Herschel discovers two satellites of themselves; in the successful application of photoUranus. Legendre and General Roy finish the graphy to the sun and moon; and above all, in connection of the observatories of Paris and Green- the marvellous results obtained by the spectrum wich. Beginning of the trigonometrical survey in England. Herschel's first observations with his forty-foot telescope.

1789. Herschel measures the rotation of Saturn, and discovers the first and second satellites of Saturn.

1790. Herschel determines the rotation of Saturn's ring, and discovers two inore satellites of Uranus.

analysis in ascertaining the substances of which the sun and other heavenly bodies consist. These matters are duly noticed in such articles as COMETS, PLANETS, SPECTRUM ANALYSIS, and SUN. Admirable and extensive catalogues of stars, double stars, and nebulæ have been made, and the optical and other instruments in use have been brought as near perfection as possible. The results of the various expeditions sent to observe the transit of Venus, December 9, 1874, have already had great

1792. Beginning of the French survey. 1794. Herschel discovers the fifth and sixth influence on astronomical calculations. satellites of Uranus.

1795. Herschel's observations on variable stars, and separation of the milky way into stars.

1796. Establishment of the French Institute. Herschel gives strong presumptions that the rotations of Jupiter's satellites are of the same duration as their orbital revolutions.

1797. Laplace's theory of tides.

1798. Cavendish demonstrates and measures the mutual attraction of metal balls, and finds the earth's density.

1799. Commencement of the 'Mécanique Céleste.'

1801. Piazzi discovers the planet Ceres. 1802. Olbers discovers the planet Palias. 1803. Herschel observes the changes in the position of double stars.

1804. Harding discovers the planet Juno. 1806. Completion of the French survey by Méchain and Delambre. Herschel suspects the motion of the whole solar system towards the constellation Hercules.

1807. Olbers discovers the planet Vesta. 1814. Piazzi's catalogue of 7646 stars. 1818. Pons discovers a comet of short period, now called by the name of Encke.

1845. Encke discovers Astrea between Jupiter and Mars.

(Elementary Lessons in Astronomy, by J. Norman Lockyer, London, 1868; Sir John Herschel's Outlines; Arago's Popular Astronomy; Whewell's History of the Inductive Sciences; Grant's History of Physical Astronomy; Laplace's Mécanique Céleste; Delambre's Astronomie; Jahn's Geschichte der Astronomie; Maedler's (German) History of Astronomy, Braunschweig, 1873.)

ASTRUC, JOHN, a French physician of great eminence, was born at Sauve, in Languedoc, in the year 1684: he studied in the University of Montpelier, and took the degree of doctor in medicine in 1703. In 1706, being then only twenty-two years of age, he began to teach medicine in the same university, acting as substitute to Chirac, one of its professors, who had been forced to attend the French army. In 1710 Astruc obtained the chair of anatomy and medicine in the University of Toulouse. He was afterwards recalled to Montpelier, where he occupied a medical chair from 1715 to 1728, when he resorted to Paris, and was induced to accept the situation of first physician to the King of Poland and Elector of Saxony. In 1730 he was appointed a consulting physician to the King of France, and in 1731, professor of medicine in the College of France. He became a member of the medical faculty of Paris in 1743, and died in 1766, at the advanced age of 82.

1846. Discovery of the planet Neptune. The discovery of this planet was unquestionably Astruc does not seem to have been endowed one of the greatest triumphs which scientific as- with an intellect of a very superior cast, and no tronomy ever achieved. From irregularities ob- great discovery is attached to his name; neverserved in the motion of the planet Uranus, it had theless, he acquired great celebrity among his conbeen conjectured that some disturbing cause, not temporaries, both as a teacher and as an author; discovered, was acting upon it. Two astronomers, and the integrity of his character was justly M. Le Verrier, in Paris, and Mr. J. C. Adams, of appreciated. A simple and happy method in Cambridge, independently of each other, calculated treating the subjects which he taught, in easy, where this disturbing cause must be situated. The clear, and eloquent language, recommended him as results of Mr. Adams' investigations were first a lecturer. His writings displayed a solid and completed, but those of M. Le Verrier were first extensive acquaintance with the history of literamade public; and acting on his information Dr., ture and science, unusual among his countrymen