had twice risen in the west, are, so far as their credit goes, confirmations of the opinion generally formed of Egyptian astronomy. With regard to the astronomy of the Greeks previously to the earliest extant works, there is little to be said. The Ionian school, founded by Thales B.C. 600, followed in succession by Anaximander, Anaximenes, and Anaxagoras, added little or nothing to practical astronomy. If Thales really predicted the total eclipse of the sun, B.C. 585 [ECLIPSES], he must have succeeded in doing so by means of the Chaldean Saros, or period of 18 years and 10 days, which produces a regular recurrence of solar and lunar eclipses. The opinion of the earth's motion attributed to Anaximander rests on slender foundation. The school of Croton, founded by Pythagoras about the year B.C. 500, and sustained by Philolaus, produced no observers, though it certainly adopted the opinion of the earth's motion. Pythagoras is said to have first taught that Lucifer and Hesperus, or the morning and the evening star, are in reality one and the same planet. The following is a list of ancient philosophers to whom the opinion of the earth's motion has been attributed : Pythagoras. Anaximander. Nicetas of Syracuse. Cleanthes the Samnite. Ecphantus. Heraclides of Pontus. Meton, B.C. 432, introduced the Luni-Solar cycle of nineteen years. In conjunction with Euctemon, he observed a solstice at Athens in the year B.C. 424. Calippus, B.C. 330, introduced the improvement of the Eudoxus of Cnidos, B.C. 370, Metonic cycle, known by his name. brought into Greece according to Pliny, the year of 365 days, and wrote some works, one of which exists in the poetical version of Aratus. Pytheas, about the time of Alexander, measured the latitude of Marseille with tolerable accuracy. The work of Aristotle on astronomy is lost; and what is still more to be regretted, that of his disciple Eudemus on the history of astronomy. The poem on the Sphere attributed to Empedocles, B.C. 450, is probably much more modern. We now come to the period of history, and of the Alexandrian school. This article being for reference only, we shall condense as much as possible the principal discoveries of the succeeding astronomers, in order of time. This could not be done in the chain of surmises mixed with history which we have just finished, since it is important to avoid confounding what is known with what is only supposed. List of astronomers of the Alexandrian school: Paulus of Alexandria. Autolycus, B.C. 300. His books are the earliest which are extant in the Greek language on astronomy. They are two: 1. On the sphere in motion. 2. On the rising and setting of the stars. He appears have considered the year as exactly 365 days. to Timocharis and Aristyllus, B.C. 300 (?), made the observations which afterwards enabled Hipparchus to discover the precession of the equinoxes. Euclid of Alexandria, B.C. 300. The Elements of Euclid' show that the Greeks of his time had no trigonometry. There is another work attributed to him, entitled 'Phenomena,' which is no more than a treatise on the doctrine of the sphere. Aratus of Cilicia, B.C. 281, has left an astronomical poem, chiefly taken from Eudoxus, and valuable on account of the commentary of Hipparchus. Many other ancient writers have also written commentaries on the poem of Aratus. The following list of them is given by De Chales : Callistratus Tenedos. The two Didymi. Numenius Parmenides. Pyrrhus of Magnesia. Aristarchus of Samos, B.C. 280. His work on the magnitudes and distances of the sun and moon is the first attempt to measure the relative distances of these two bodies, by observing their angular dis ASTRONOMY. To him also is attributed the opinion that the earth revolves round the sun. tance at the time of half moon. Manetho the Egyptian, B.C. 260. His history is lost, but a poem attributed to him remains. It is a description of the heavens, filled Eratosthenes of Cyrene, B.C. 240, is said to have observed with some with astrology and containing no observations. celebrated astrolabes which he erected at Alexandria, which remained standing till the time of Ptolemy. Various works are attributed to him, for which see his Life, in the BIOG. DIV. He observed (either with a gnomon or with a meridian circle) [ASTROLABE] the obliquity of the ecliptic, and the latitude of Alexandria; and from the latter, and the fact that at Syene the sun was vertical at the summer solstice, he deduced an approximation to the earth's magnitude. His approximation makes a degree to be 700 stadia. A catalogue of stars attributed to him (the oldest extant) is probably spurious, but shows that, in and about his time, the method of referring stars to their latitudes and longitudes was not practised. His value of the obliquity of the ecliptic-11 parts out of 166 of the whole circumference-was adopted by Hipparchus and Ptolemy. Archimedes of Syracuse, died B.C. 212. He observed solstices, and His writings show that attempted to measure the sun's diameter. trigonometry was as yet unknown. 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 comparing his own observations with those of Aristyllus and Timocharis, or others of his predecessors. He was the first who employed processes analagous to those of plane and spherical trigonometry, for which he constructed a He first used right ascensions and declinations, which table of chords. he afterwards abandoned in favour of latitudes and longitudes. He suggested the method of referring terrestrial positions to latitude and longitude, and was probably the inventor of the stereographic projection. He determined the mean motion of the sun and of its apogee, the inequality of the sun's motion, and the length of the year, to His greater exactness than his predecessors. He found the mean motion of the moon, of her nodes, and of her apogee; her parallax, eccentricity, the equation of her centre, and the inclination of her orbit. observations also led him to suspect another inequality in the moon's motion, which Ptolemy afterwards discovered (the evection). calculated eclipses, and used the results in the improvement of the 'Elements.' He made one of the first steps towards a correct representation of phenomena, by supposing the sun to move round the earth in a circle, the earth not being at the centre. His catalogue of the longitudes and latitudes of 1081 stars was the first at all worthy of If Hipparchus had possessed the pendulum and the telescope, fifty years might have enabled his successors to place astronomy in the state in which it stood at the birth of Newton. Considering his means, his observations are perhaps unequalled. the name. He After the death of Hipparchus there is no astronomer of eminence till Ptolemy. Between them we have Hypsicles of Alexandria, B.C. 146, wrote the 14th and 15th books of the Elements of Euclid,' which contain some astronomical propositions. Geminus (of Rhodes ?) B.C. 70, wrote an introduction to the heavenly phenomena, containing no new discovery. It would seem he was not an observer. Posidonius about the same time attempted to verify the measure of the earth of Eratosthenes. His writings are all lost, but many of his opinions are preserved in Cleomedes and Strabo. He remarked (though probably he was not the first who did so) the connection of high water with the southing of the moon. Theodosius of Bithynia, B.C. 50, left a work on spherical geometry, another on climates, and a third on the phenomena of day and night. Sosigenes of Alexandria, B.C. 50, corrected the calendar under Julius Cæsar. Hyginus left an astronomical description of the heavens. Manilius, a Roman, A.D. 10, wrote an astronomical and astrological poem. Seneca, A.D. 50. His book on natural philosophy contains many pieces of information on astronomical history, but is principally remarkable for the bold opinions of the author on the nature of comets. These he declares to be planets, whose laws he predicted would one day be calculated, and that posterity would wonder how things so simple could have so long escaped notice. Menelaus, A.D. 80, observed at Rome and Rhodes. He has left three books of spherical trigonometry. Theon of Smyrna, A.D. 117 (?) observed at Alexandria. He wrote on astronomy, and made a collection of astronomical works. His observations are cited by Ptolemy. Cleomedes wrote on astronomy. He certainly lived after Posidonius, but whether before or after Ptolemy is uncertain. He is usually considered as having lived under Augustus Cæsar. We must suppose that there were many real observers between the epochs of Hipparchus and Ptolemy; but from the loss of even their names, and the silence of Ptolemy himself, it is clear that no discovery of any importance was made. Ptolemy of Alexandria, A.D. 130-150. We must briefly mention his works, his system, and his discoveries. The μаonμaríkη σúvražis, or mathematical collection, afterwards called μeyáλn oúvražıs, and by the Arabs the Almagest [ALMAGEST; SYNTAXIS] is the work from which we derive most of our knowledge of the Greek astronomy. We find there a full account of the observations and discoveries of Hipparchus; those of Ptolemy himself; the reasons and elements of his system; various mechanical arguments against the motion of the earth, which show that the first principles of dynamics were utterly unknown; a description of the heavens and the Milky Way, and a catalogue of stars, which we may be nearly certain was that of Hipparchus, reduced to his own time by an assumed value for the precession, but which has been asserted to have been corrected by new observations; a theory of the planetary motions; the length of the year; the instruments he employed, &c. The Ptolemaic system [for more detail of which see PTOLEMAIC SYSTEM] was an attempt to represent the motions of the planets by supposing them to move uniformly in circles, the centres of which circles themselves moved uniformly in circles round the earth. The angular motions of the planets, as then known, were sufficiently well represented by this system; not so their changes of distance from the earth, as seen in their apparent diameters. This was the universal system of after-times till Copernicus. The principal discovery of Ptolemy is that of the LUNAR EVECTION (which see), 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 (which see), 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 Hipparchus. He entered into the investigation of every point which Hipparchus had touched; in some instances finding more correct values; in others, altering without amending. He was not an astronomer only, but wrote on geography, music, chronology, mechanics, and, unfortunately, on astrology. With Ptolemy the originality of the Greek school ends. We must come to the Arabs before we find anything worth particular notice. Sextus Empiricus, A.D. 173, described and wrote against the Chaldean astrology. Censorinus, A.D. 238, wrote an astrological work on the day of nativity, containing historical information with regard to astronomy. Julius Firmicus Maternus, A.D. 370, wrote on astronomy. Pappus of Alexandria, A.D. 383. His commentary on Ptolemy is nearly all lost. Theon of Alexandria, A.D. 385, the most celebrated commentator on Ptolemy. He was a good mathematician, but no great astronomer. He has however left some tables, and a method of constructing almanacs. Hypatia (his daughter), murdered A.D. 415, the first female on record celebrated for her scientific talents. She wrote one book of her father's commentary, and constructed some tables. Martianus Capella, A.D. 470, in his 'Satyricon,' has some astronomical notions, among which is the following: that Mercury and Venus move round the sun. Cicero and Macrobius give the same idea; but the passage of Martianus is remarkable as being reported to have turned the attention of Copernicus to the system which bears his name. Thius of Athens, A.D. 500, has left six observations of lunar occultations and solstices: the only observations recorded between Ptolemy and the Arabs. Simplicius, A.D. 546, has left a commentary on, and description of, the astronomical work of Aristotle, which we have mentioned as lost. Proclus Diadochus (the commentator of Euclid), A.D. 550, wrote a commentary on the astrology of Aristotle, and a description of astronomical phenomena. Isidore, archbishop of Hispalis (Seville), A.D. 636, wrote a theological work on astronomy. Bede, A.D. 720, and Barlaam the monk, A.D. 1330, are attached to the preceding by Delambre. Both wrote astronomical works of little distinct merit. The last Greek writer on astronomy of the least note is Michel Psellus, A.D. 1050. It is remarkable that, excepting his own commentators, few of the authors who flourished during the period immediately succeeding ever quote Ptolemy. Had it not been for the Arabs, the writings of the latter must have been lost. The Alexandrian school was destroyed by the Saracens under Omar, A.D. 640; and the rise of astronomy among the eastern Saracens dates from the building of Bagdad by the Caliph Al Mansur, in the year 762. In the reign of this prince translations of the Greek writers were begun; and, with nearly the same instruments and the same theory as Ptolemy, a career of four centuries of observation commenced, during which many astronomical elements, and in particular the obliquity of the ecliptic, and the precession of the equinoxes, were more accurately determined. In the reign of Al Mamoum, 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. Albategnius, or Al-Batani, A.D. 880, discovered the motion of the blar apogee, corrected the value of the precession, the solar eccentricity, and the obliquity of the ecliptic, and published tables. He is the first who made use of sines (instead of chords) and versed sines. He found the length of the year more accurately. He is, beyond all doubt, the only distinguished observer of whom we know anything between Hipparchus and Tycho Brahé. Alfraganus, or Al-Fergadi, and Thabet ben Korrah, both about A.D. 950. The first has left a work on astronomy; the second is principally remarkable by his having revived an old notion of the Greeks (not mentioned by Ptolemy, but by Theon) of a variation in the position of the ecliptic, which has been called a trepidation. (See 'Hist. Ast.,' Library of Useful Knowledge, p. 33.) Ebn Yunis, and Abul-Wefa, about A.D. 1000. The former, an Egyptian, an observer and mathematician of great merit, has left a work containing tables and observations. He first noted the time of the beginning and end of an eclipse by taking the altitude of a star. His work shows an increasing knowledge of trigonometry. He was the first who employed subsidiary angles. Abul-Wefa first formally used tangents, cotangents, and secants, which Albategnius had overlooked. He gave tables of tangents and cotangents. Alphetragius of Morocco, 1050, attempted a new explanation of the planetary motions, not worthy of further notice. Arsachel, a Spanish Moor, 1080, has left some tables [TOLEDO, TABLES OF] of indifferent accuracy. His contemporary, Alhazen, wrote on refraction. Geber, also a Spaniard (about 1080?), made some improvements in spherical trigonometry. He introduced the use of the cosine. Abul Hassan, about 1200, has left a catalogue of stars, and some improvements in dialling. We have Persian tables (of the 11th century?) translated by George Chrysococca, a Greek physician, in the 14th century; but the best known are those of Nasireddin, published in 1270, under the protection of Hulagu, grandson of Jenghis Khan, and conqueror of Persia. The Persians have a method of intercalating their solar years, which, though complicated, is of surprising accuracy, but when they first began to employ it is unknown. [CALENDAR.] Ulug Beg, grandson of Timur, 1433. This 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 geographical latitudes and longitudes. The Emperor Akbar (sixth from Timur, died 1605) also encouraged astronomy, and caused many Hindoo works to be translated into Persian. In China, Cocheou-King 1280, patronised by Kublai, brother of Hulagu, and fifth successor of Jenghis Khan, in the partial conquest which that prince made of China, made a great number of good observations. He introduced spherical trigonometry, and rejected the ancient chronology. Since the 15th 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 1230. Sacrobosco (an Englishman named Holywood), 1220, wrote a work on the sphere taken from Ptolemy, &c. It continued for a long time in great repute. He also wrote on the Calendar. About the same time, Jordanus wrote a curious work on the Planisphere. Alonso X., king of Castile, 1252, with the assistance of Arabs and Jews, formed the first European tables. They differ little from those of Ptolemy. [ALONSINE TABLES.] Roger Bacon, 1255, wrote on the phenomena of astronomy. (For writers of this period, not worth naming, see Delambre,' Hist. Ast. Moy.' pp. 258, 444.) The Cardinal Cusa, 1440, wrote on the correction of the Calendar. He is said to have maintained the motion of the earth. George Purbach, 1460, extended trigonometrical tables, and published a theory of the planets based on that of Ptolemy. John Müller, called Regiomontanus (died 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. The two last-mentioned writers deserve some special notice, though it cannot be said that they made any direct advances either in theory or observation. Their writing, and the facilities afforded by their tables, undoubtedly did much to promote a taste for astronomy. George of Trebizond, called Trapezuntius, who died 1486, first translated the Almagest' from the Greek into Latin. Bianchini, 1495, published tables similar to those of Alonso. Waltherus (died 1504), a pupil of Regiomontanus, made numerous observations which were often reprinted. The following names are inserted that the reader may know to what names to refer for the astronomy of the time immediately preceding the promulgation of the system of Copernicus. Except in this point of view, there is but little interest attached to their labours :Riccius, 1521, wrote a work on astronomy, containing much historical discussion. Werner (died 1528), gave a more correct value of the precession. 667 ASTRONOMY. ASTRONOMY. Stöffler (died about 1531), published almanacs for fifty years; wrote The Copernican theory had its advocates, but was not yet adoptel by on the astrolabe, &c. Munster (died 1552), wrote on clocks and dials. In 1528, Fernel, who died in 1558, gave a very correct measure of a 1140. Occurrence of a total eclipse of the sun which was visible in London. This eclipse is mentioned in the Saxon Chronicle and in the writings of William of Malmesbury. 1264. Apparition of a great comet in the heavens, accompanied by a tail 100° in length. 1402. Two great comets appeared in the heavens in the course of this year. 1433. Occurrence of a total eclipse of the sun which was visible in Scotland. 1456. Apparition of a great comet which spread universal terror throughout Europe. This is known to have been one of the apparitions of Halley's comet. 1468. A great comet visible: observed in Europe and China. 1472. A great comet observed both in Europe and China. In one day it described an arc of 40°. Copernicus, born 1473, died 1543. Applied himself to astronomy from 1500. In 1530, he had finished his tables of the planets, and his work On the Revolutions of the Heavenly Bodies,' containing an explanation of the COPERNICAN SYSTEM, which, it is almost unnecessary to say, was a revival of the opinions of the Pythagorean school on the motion of the earth. It was published in 1543, and its author died immediately afterwards. Copernicus improved the lunar tables, and gave, to a considerable extent, an explanation of celestial phenomena upon his own system. His book is a mixture of his own original and sagacious notions and of the old philosophy; 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 more than the names of many astronomers. The following is the list of those who are worth mention between Copernicus and the death of Tycho Brahé. The history of this period has been elucidated chiefly by Professor De Morgan. The dates are generally those of death, but where that is not known, the date in brackets is that of the publication of some work. .(1578) many. Algebra had been introduced into most parts of Europe, but now come. Tycho Brahe, born 1546, began to study astronomy 1560; commenced 1582; was driven from thence, 1597; died 1601. He made a catalogue his observations at Huena, an island, in the Baltic, near Copenhagen, of the fixed stars, more accurate than any which preceded: gave the (which see) of the moon, the variation of the motion of her nodes, and first table of refractions: discovered the variation and annual equation as any of the preceding, he discarded the trepidation of the precession, of the inclination of her orbit. What was essentially as great a service time; he also ascertained that comets (those of his day, of course) already mentioned, which had more or less infected all tables up to his were further removed from the earth than the moon; in fact, that they had no parallax which his instruments could discover, thus refuting the notion that they were atmospheric bodies. He greatly improved observation. and extended the instruments in use as well as all the methods of Tycho Brahé did not admit the Copernican theory; but substituted for it one of his own, usually known by the name of the Tychonic system. This consisted in supposing the sun to move round the earth, with it round the earth. This system explains all the appearances as but all the other planets to move round the sun, being also carried well as that of Copernicus; and we must say (though it is always usual to reproach Tycho for refusing to admit the simple system of Copernicus) that by this means the then unanswerable arguments against the Copernican system were avoided. In fact, there is nothing but the aberration of light (a comparatively recent discovery), which is demonstrably conclusive in favour of the annual motion of the earth. to have been promulgated by some of the ancients, at least with regard [ABERRATION; MOTION (APPARENT).] The system of Tycho is said The reformation (as it was called) of the calendar took place in 1582, to the inferior planets. As the views of those who made the change were rather theological than astronomical, we shall only here under Pope Gregory XIII. mention the fact and the disputes it gave rise to; referring for further information to CALENDAR. From the time of the death of Tycho Brahé, to that of Newton, To enable the which forms the next great epoch in the history of astronomy, we can only dwell generally on a few leading discoveries. deaths of Tycho Brahé and Newton, which Delambre has thought reader to search further, we give a table of all the names between the worthy of any mention, with some few additions. The names mentioned from 1581 to 1727, which are not in this list, will be found in the next. The year of death is given opposite to each name; or where that is not known, the year of some publication is given in brackets. The dates are principally from Weidler, and several from Delambre, compared with those in the first edition of Lalande's Astronomy. Piccolomini 1553 Didacus à Stunica 1584 Orontius Fineus 1555 Urstisius 1588 Gemma Frisius. Royas .(1555) Benedict . 1590 Vieta Dee .(1556) Schöner 1590 Gilbert 1603 Peyresc 1637 Reinerius 1639 . Field . (1556) Landgrave of Hesse Cassel 1592 Bassantin 1557 Mercator 1594 Recorde. 1558 Thomas Digges . (1595) Nunez .(1605) Horrocks 1641 1609 Galileo 1642 1612 Gascoigne. 1644 Carelli 1558 Rothmann 1596 Pitiscus 1613 Herigonius Vinet 1564 Patricius Leonard Digges 1571 Galucci. Calvisius 1615 Langrenus. .(1644) 1644 1615 Bartoli . (1644) Ramus 1598 Wright 11615 Rheita .(1645) Maurolicus 1575 Jordanus Brunus . 1600 Fabricius 1616 Fontana .(1646) Rheticus . 1576 Tycho Brahé € 1601 Nonius. . 1577 Magini 1617 Cavalerius. 1647 1617 Longomontanus 1647 Ursinus. . (1619) Torricelli 1647 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. Jordanus Brunus, who was burnt to death at Rome in consequence of his bold opinions on the system of the universe. 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. Tarde Wendelinus Kepler .(1620) Durret .(1649) Marius 1624 Argoli 1650 Adr. Romanus 1625 Descartes 1650 Gunter 1626 Scheiner 1650 Snellius . (1651) .(1626) Petavius 1652 .(1628) Crabtree 1652 .(1628) Pascal 1653 . 1630 Gassendi 1655 . 1630 Licetus 1656 Morinus 1656 1660 € 1631 1632 Street 1633 Levera . (1663) Cunitia (Maria) 1664 Byrgius 1633 Norwood .(1633) Habrecht 1634 Deusingius Lubienietsky. Townley 1666 (1667) .(1670) As we approach an age in which discoveries proceed rapidly, it would disturb the order of time if we were to enumerate those of individuals together. We shall therefore give the dates in chronological order of the more remarkable phenomena which have appeared, and of the principal accessions to the science, keeping, according to our original plan, only enough to direct the attention of the reader to points worthy of further reference. 1560. Occurrence of a total eclipse of the sun which was observed at Coimbra by Clavius. 1567. Occurrence of an annular eclipse of the sun. 1572. Apparition of a new star in the constellation Cassiopeia. Hagecius determines the apparent positions of the new star of this year by measuring its altitude on the meridian and noting the time of observation. 1573. Thomas Digges proposes to determine the positions of the celestial bodies by the method of corresponding altitudes. 1577. Apparition of a comet, the observations of which enabled Tycho Brahé to demonstrate that cometary bodies revolve in the regions beyond the moon. 1581, or thereabouts, Galileo remarks the isochronism of the pen dulum. 1590. An occultation of Mars by Venus witnessed by Mostlin. (A doubtful observation.) 1596. Kepler's Mysterium Cosmographicum,' containing fanciful analogies between the orbits of the planets and the regular solids of geometry. 1598. Occurrence of a total eclipse of the sun which was observed in the north of Europe. 1601. Occurrence of an annular eclipse of the sun observed in Norway. 1603. Bayer's maps, in which the stars are first denoted by letters. 1604. Kepler approximates more nearly to the law of refraction. A new star appears in the constellation Serpentarius. 1607. An apparition of Halley's comet. 1608. Telescopes invented in Holland by Lipperhey, a spectacle maker. 1609. Galileo made a telescope from a general description of a magnifying instrument made by Lipperhey. He used a concave object glass, Lipperhey a convex. 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. He also discovers the diurnal libration of the moon, and that in latitude. Harriot observes the spots on the sun. (This fact has only been known from examination of Harriot's papers in the present century. It appears he got telescopes from Holland.) 1611. Lyncean academy founded. Galileo observes the spots on the sun. 1614. Napier's invention of logarithms. 1616. Prohibition of the theory of Copernicus by the Roman court. 1617. Snellius measures an arc of the meridian at Leyden. This was the first done by triangulation; but astronomical instruments were not yet sufficiently perfect to make this method much better than the old one. 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. Apparition of a great comet with a tail upwards of 100° in length. 1619. Snellius discovers the law of refraction from one medium into another. 1626. Wendelinus determines the diminution of the obliquity of the ecliptic. He also extended Kepler's law to Jupiter's satellites, and ascertained the sun's parallax. 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; he also measured the diameter of the planet. Vernier publishes his invention of the instrument which bears his name. 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. 1637. Horrocks suspects the long inequality in the mean motions of Jupiter and Saturn. 1638. Horrocks ascribes the motion of the lunar apsides to the disturbing force of the sun, and adduces the oscillations of the conical pendulum as an illustration of the planetary movements. 1639. Horrocks 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. Gascoigne applied the telescope to the quadrant, and a micrometer to the telescope. 1646. Fontana observes Jupiter's belts. 1647. 'Selenographia' of Hevelius, in which the moon's libration in longitude is announced. 1650. Scheiner constructs a convex object-glass telescope. 1651. A transit of Mercury observed by Shackerley, at Surat in India. 1652. A great comet visible in the heavens. 1654. Huyghens completes the discovery of Saturn's ring. 1655. Huyghens discovers a satellite of Saturn (Titan). 1657. Academia del Cimento founded. 1658. Huyghens made the first pendulum clock. 1659. Huyghens, without being aware of what Gascoigne had done, devises the original form of the micrometer as used on the continent. 1660. Mouton applied the simple pendulum to observations of differences of right ascension, and measured the sun's diameter very correctly by it. 1661. A transit of Mercury observed at Dantzig by Hevelius. 1662. Royal Society of London incorporated. Cassini begins his researches on refraction. Malvasia's improvement of Huyghens' micrometer. 1663. Gregory makes his reflecting telescope. 1664. Hooke detects the rotation of Jupiter. 1665. Cassini determines the time of rotation of Jupiter, and publishes the first Tables of the Satellites. Hooke proposes to measure the distance of the moon from the stars in her vicinity, by means of a rete or divided scale. 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 Gascoigne. Newton first turned his attention to gravitation. 1667. Auzout and Picard applied the telescope to the mural quadrant, without knowing that Gascoigne had preceded them. 'Cometo 1668. Cassini's second Tables of Jupiter's Satellites. graphia' of Hevelius. A great comet visible in southern latitudes. 1669. Newton made his first reflecting telescope. 1670. Mouton's first use of interpolations. 1671. Picard and La Hire publish their degree of the meridian, obtained by measuring from Paris to Amiens. Richer, in a voyage to Cayenne, observes the shortening of the seconds' pendulum in approaching the equator. Flamsteed begins observing at Derby. Cassini begins the observations which led to his discovery of the inclination of the lunar equator, and the coincidence of its nodes with those of the orbit. Cassini discovers a satellite of Saturn (Japhet). 1672. Cassini discovers a satellite of Saturn (Rhea). 1673. Huyghens publishes his Horologium Oscillatorium,' in which are found the first theorems on central forces and centrifugal force. Flamsteed explains the equation of time. Picard, in the course of his labours at the Royal Observatory of Paris, introduces the practice of determining the positions of the stars by observing their altitude on the meridian and noting the corresponding time. 1674. Hooke revived the idea of attraction, but without assigning any law, or connecting it with any observed facts. Spring watches made under the direction of Huyghens, who was unacquainted with what Hooke had already done in the matter. 1675. Roemer announces his discovery of the velocity of light by means of Jupiter's satellites. Greenwich Observatory founded. D. Cassini discovers the division on Saturn's ring. Roemer recognises the advantages of the transit instrument for determining the right ascensions of the stars. 1676. Flamsteed commences his observations at the Royal Observatory, Greenwich. 1677. A transit of Mercury observed at St. Helena by Halley. 1679. Halley published his Catalogue of Southern Stars, observed at St. Helena. Appearance of the Connaissance des Tems.' 1680. Flamsteed gives the law of the annual equation of the moon, and corrects the tables accordingly. A great comet appeared in the heavens. This comet is remarkable for having, on its passage of the perihelion, approached nearer the sun than any other comet recorded in history, with the exception of the great comet of 1843. It is also memorable for having conducted Newton to the important discovery that comets revolve in conic sections around the sun, conformably to Kepler's laws. Clement, a London clockmaker, introduces the use of anchor pallets in clocks. 1681. Doerfel's work on comets. 1682. An apparition of Halley's comet. 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. 1683. Cassini and La Hire discontinue till 1700 the arc begun in 1680. A mural quadrant is erected in the plane of the meridian, at the Royal Observatory of Paris. Cassini's earliest researches on the zodiacal light. 1684. Cassini discovers two satellites of Saturn (Tethys and Dione). 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. Flamsteed commences his course of observations with the mural arc. 1690. Huyghens' theoretical determination of the ellipticity of the earth. Catalogue of Hevelius published. 1693. Cassini's third tables of Jupiter's satellites. Announcement of his discoveries on libration. Halley discovers the acceleration of the moon's mean motion. 1694. Commencement of Newton's correspondence with Flamsteed respecting observations for the improvement of the lunar theory and the establishment of the theory of refraction. 1699. Occurrence of a total eclipse of the sun, visible in the North of Europe. 1700. The Cassinis (D. and J.) extend the arc which the former had begun southward. 1702. La Hire's researches on the theory of refraction. 1704. Roemer commences observing the stars with a meridian circle. 1705. Halley first predicted the return of a comet, namely, that of 1759. 1706. Occurrence of a total eclipse of the sun, which was visible in the south of France. 1711. Berlin Observatory founded. 1714. J. Cassini discovers the inclination of the orbit of Saturn's fifth satellite. 1715. Occurrence of a total eclipse of the sun, which was visible in London. Taylor's researches on the theory of refraction. 1718. Bradley publishes his tables of Jupiter's satellites. J. Cassini and Maraldi complete at Dunkirk the arc begun by Cassini. 1719. Maraldi's (I.) researches on the rotation of Jupiter. 1721. Halley communicates to the Royal Society Newton's Table of Refractions. 1724. Occurrence of a total eclipse of the sun, which was visible in Paris. 1725. Flamsteed's Historia Colestis.' Petersburg Observatory founded. Harrison's compensation pendulum. 1726. Bianchini determines the rotation of Venus. Graham invents the mercurial pendulum. 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 of the preceding table 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 done more for astronomy than the mathematical Syntaxis of Ptolemy, had it been similarly circumstanced: that is, the work of Ptolemy 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. [FLAMSTEED, in BIOG. DIV.] 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 Hooke, 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 Copernican, when they speak of Newton as the establisher of the latter. After what we have said, it is unnecessary to discuss this further than to observe, that it was Galileo who destroyed the mechanical objections to the notions of Copernicus, 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 (which see), furnished the direct and | unanswerable proof of the earth's annual 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. We shall now proceed to sketch the annals of astronomy from the death of Newton to the present time. 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 methodise, the results of the first. The following is the list of names from the death of Newton to the close of the 18th century, arranged in the same manner as the preceding : 1728. Observatory of Copenhagen destroyed by fire; the great mass of observations executed by Roemer and his successor, Horrebow, irrecoverably lost. 1729. A comet visible for six months, remarkable for its perihelion distance being greater than that of any other comet recorded in history. Bouguer's researches on astronomical refraction. 1731. Hadley's quadrant invented. 1732. Maraldi (II.) improves the theory of the satellites of Jupiter by observation. The introduction, by Maupertius, of the Newtonian theory into France. Wright's Lunar Tables. 1733. Occurrence of a total eclipse of the sun, which was visible in the northern countries of Europe. 1736. Maupertius, &c., measure an arc in Lapland, and Bouguer and La Condamine in Peru. 1737. Lacaille and Cassini de Thury re-measure the arc of D. Cassini. Clairaut improves the theory of the figure of the earth. An annular eclipse of the sun observed in Scotland. 1739. Dunthorn's Lunar Tables. 1740. J. Cassini's Astronomy published, containing many new tables from his own and his father's observations. 1744. Euler's Theoria Motuum,' &c., the first analytical work on the planetary motions. Apparition of a splendid comet which was visible in full daylight. 1745. Bradley discovers the phenomenon of nutation. Bird began to improve the graduation of mathematical instruments. 1746. Euler's Solar and Lunar Tables. Wargentin's Tables of Jupiter's satellites. 1747. Euler, Clairaut, and D'Alembert. Various researches in the planetary theory. Mayer's confirmation of Cassini's theory of libration, by observation. 1748. Bouguer proposes a micrometer with a divided object-glass |