ASTRONOMY

, the doctrine of the heavens, and their phenomena.

Astronomy is properly a mixed mathematical science, by which we become acquainted with the celestial bodies, their motions, periods, eclipses, magnitudes, distances, and other phenomena. Some, however, understand the term astronomy in a more extensive sense, as comprising in it the theory of the universe, with the primary laws of nature: in which sense it seems to be rather a branch of physics than of mathematics.

History of Astronomy.

The invention of astronomy has been variously given, and ascribed to several persons, several nations, and several ages. Indeed it is probable that mankind never existed without some knowledge of astronomy amongst them. For, besides the motives of mere curiosity, which are sufficient of themselves to have excited men to a contemplation of the glorious and varying celestial canopy, it is obvious that some parts of the science answer such essential purposes to mankind, as to make the cultivation of it a matter of indispensable necessity. Accordingly we find traces of it, in different degrees of improvement, among all nations.

Adam, in his state of innocence, it is supposed by some of the Jewish rabbins, was endowed with a knowledge of the nature, influence, and uses of the heavenly bodies; and Josephus ascribes to Seth and his posterity a considerable knowledge of astronomy: he speaks of two pillars, the one of stone and the other of brick, called the pillars of Seth, upon which they engraved the principles of the science; and he says that the former was still entire in his time. But be this as it may, it is evident that the great length of the antediluvian lives would afford such excellent opportunities for observing the heavenly bodies, that we cannot but suppose that the science of astronomy was considerably advanced before the flood. Indeed Josephus says that longevity was bestowed upon them for the very purpose of cultivating the sciences of geometry and astronomy; observing that the latter could not be learned in less than 600 years; “for that period, he adds, is the grand year.| An expression remarkable enough; and by which it may be supposed is meant the period in which the sun and moon come again into the same situation in which they were at the beginning of it, with regard to the nodes, apogee of the moon, &c. “This period, says Cassini, of which we find no intimation in any monument of any other nation, is the finest period that ever was invented: for it brings out the solar year more exactly than that of Hipparchus and Ptolemy; and the lunar month within about one second of what is determined by modern astronomers.” If the Antediluvians had such a period of 600 years, they must have known the motions of the sun and moon more exactly than their descendants knew them some ages after the slood.

On the building of the Tower of Babel, it is supposed that Noah retired with his children, born after the flood, to the north-eastern part of Asia, where his descendants peopled the vast empire of China. And this, says Dr. Long, “may perhaps account for the Chinese having so early cultivated the study of astronomy, &c.” It is said that the Jesuit missionaries have found traditional accounts among the Chinese, of their having been taught this science by their first emperor Fo-hi, who is supposed to be the same with Noah; and Kempfer asserts that Fo hi discovered the motions of the heavens, divided time into years and months, and invented the 12 signs into which they divide the zodiac, and which they distinguish by these names following; 1, the mouse; 2, the ox or cow; 3, the tiger; 4, the hare; 5, the dragon; 6, the serpent; 7, the horse; 8, the sheep; 9, the monkey; 10, the cock or hen; 11, the dog; and, 12, the boar. They divide the heavens into 28 constellations, or classes of stars, allotting 4 to each of the 7 planets; so that the year always begins with the same planet; and their constellations answer to the 28 lunar mansions used by the Arabian astronomers. These constellations however they do not mark with the figures of animals, like most other nations, but by connecting the stars by straight lines, and denoting the stars themselves by small circles: so, for instance, the great bear would be marked thus, The Chinese themselves have many records and traditions of the high antiquity of their astronomy; though not without suspicion of great mistakes. But, on more certain authority, it is asserted by F. Gaubil, that at least 120 years before Christ, the Chinese had determined by observation the number and extent of their constellations as they now stand; the situation of the fixed stars with respect to the equinoctial and solstitial points; and the obliquity of the ecliptic; with the theory of eclipses: and that they were, long before that, acquainted with the true length of the solar year, the method of observing meridian altitudes of the sun by the shadow of a gnomon, and of deducing from thence his declination, and the height of the pole. The same missionary also says, that the Chinese have yet remaining some books of astronomy, which were written about 200 years before Christ; from which it appears, that the Chinese had known the daily motion of the sun and moon, and the times of the revolutions of the planets, many years before that period.

Du Halde informs us, that Tcheou cong, the most skilful astronomer that ever China produced, lived more than a thousand years before Christ; that he passed whole nights in observing the celestial bodies, and arranging them into constellations, &c. At present however, the state of astronomy is but very low in that country, although it be cultivated at Peking, by public authority, in like manner as in most of the capital cities of Europe.

The inhabitants of Japan, of Siam, and of the Mogul's empire, have also been acquainted with astronomy from time immemorial; and the celebrated observatory at Benares, is a monument both of the ingenuity of the people, and of their skill in that science.

According to Porphyry, astronomy must have been of very ancient standing in the East. He informs us that, when Babylon was taken by Alexander, there were brought from thence celestial observations for the space of 1903 years; which therefore must have commenced within 115 years after the flood, or within 15 years after the building of Babel.—Epigenes, according to Pliny, affirmed that the Babylonians had observations of 720 years engraven on bricks.—Again, Achilles Tatius ascribes the invention of astronomy to the Egyptians; and adds, that their knowledge of that science was engraven on pillars, and by that means transmitted to posterity.

M. Bailly, in his elaborate History of ancient and modern astronomy, endeavours to trace the origin of this science among the Chaldeans, Egyptians, Persians, Indians and Chinese, to a very early period. And thence he maintains, that it was cultivated in Egypt and Chaldea 2800 years before Christ; in Persia, 3209; in India, 3101; and in China, 2952 years before that æra. He also apprehends, that astronomy had been studied even long before this distant period, and that we are only to date its revival from thence.

In investigating the antiquity and progress of astronomy among the Indians, M. Bailly examines and compares four different sets of astronomical tables of the Indian philosophers, namely that of the Siamese, explained by M. Cassini in 1689; that brought from India by M. le Gentil of the Academy of Sciences; and two other manuscript tables, found among the papers of the late M. de Lisle; all of which he found to accord together, and all referring to the meridian of Benares, above-mentioned. It appears that the fundamental epoch of the Indian astronomy, is a conjunction of the sun and moon, which took place at the amazing distance of 3102 years before Christ: and M. Bailly informs us that, by our most accurate astronomical ta bles, such a conjunction did really happen at that time. He further observes that, at present, the Indians calculate eclipses by the mean motions of the sun and moon observed 5000 years since; and that their accuracy, with regard to the solar motion, far exceeds that of the best Grecian astronomers. They had also settled the lunar motions by computing the space through which that luminary had passed in 1,600,984 days, or a little more than 4383 years. M. Bailly also informs us, that they make use of the cycle of 19 years, the same as that | ascribed by the Greeks to Meton; that their theory of the planets is much better than Ptolemy's, as they do not suppose the earth in the centre of the celestial motions, and believe that Venus and Mercury move round the sun; and that their astronomy agrees with the most modern discoveries as to the decrease of the obliquity of the ecliptic, the acceleration of the motion of the equinoctial points, &c.

In the 2d vol. of the Transactions of the Royal Society of Edinburgh is also a learned and ingenious dissertation on the astronomy of the Brahmins of India, by Mr. Professor Playfair; in which the great accuracy and high antiquity of the science, among them, is reduced to the greatest probability. It hence appears that their tables and rules of computation, have peculiar reference to an epoch, and to observations, 3 or 4 thousand years before Christ; and many other instances are there adduced, of their critical knowledge in the other mathematical sciences, employed in their precepts and calculations.

Astronomy, it seems, too, was not unknown to the Americans; though in their division of time, they made use only of the solar, and not of the lunar motions. And that the Mexicans, in particular, had a strange predilection for the number 13, by means of which they regulated almost every thing: their shortest periods consisted of 13 days; their cycle of 13 months, each containing 20 days; and their century of 4 periods, of 13 years each: and this excessive veneration for the number 13, arose, according to Siguenza, from its being the number of their greater gods. And it is very remarkable, that the Abbé Clavigero asserts it as a fact, that, having discovered the excess of a few hours in the solar above the lunar year, they made use of intercalary days, to bring them to an equality, as established by Julius Cæsar in the Roman Calendar; but with this difference, that, instead of one day every 4 years, they interposed 13 days every 52 years, which produces the same effect.

Most authors however fix the origin of astronomy and astrology, either in Chaldea or in Egypt; and accordingly among the ancients we find the word Chaldean often used for astronomer, or, which was the same thing, astrologer. Indeed both of these nations pretended to a very high antiquity, and claimed the honour of producing the first cultivators of this science. The Chaldeans boasted of their temple or tower of Belus, and of Zoroaster, whom they placed 5000 years before the destruction of Troy; while the Egyptians boasted of their colleges of priests, where astronomy was taught, and of the monument of Osymandyas, in which, it is said, there was a golden circle of 365 cubits in circumference, and one cubit thick, divided into 365 equal parts according to the days of the year, &c.

It is, indeed, evident, that both Chaldea and Egypt were countries very proper for astronomical observations, on account of the extended flatness of the country, and the purity and serenity of the air. The tower of Belus, or of Babel itself, of a great height, was probably an astronomical observatory; and the lofty pyramids of Egypt, whatever they were originally designed for, might perhaps answer the same purpose; and at least they shew the skill of this people in practical astronomy, as they are all placed with their four fronts exactly facing the cardinal points of the compass. The Chal deans certainly began to make observations soon after the confusion of languages, as appears from the observations found there on the taking of Babylon by Alexander; and it is probable they began much earlier. It hence appears that they had determined, with tolerable exactness, the length both of a periodical and synodical month. They had also discovered, that the motion of the moon was not uniform; and they even attempted to assign those parts of the orbit in which the motion is quicker or slower. We are also assured by Ptolemy that they were not unacquainted with the motion of the moon's apogee and nodes, the latter of which they supposed made a complete revolation in 6585 1/3 days, or a little more than 18 years, and contained 223 complete lunations, which period is called the Chaldean Saros. From Hipparchus, the same author also gives us several observations of lunar eclipses made at Babylon above 720 years before Christ. And Aristotle informs us, that they had many occultations of the planets and sixed stars by the moon; a circumstance which led them to conceive that eclipses of the sun were to be attributed to the same cause. They had also no inconsiderable share in arranging the stars into constellations. Nor had even those eccentric bodies the comets escaped their observation: for both Diodorus Siculus and Appollinus Myndicus, Seneca informs us, accounted these to be permanent bodies, having stated revolutions as well as the planets, but in much more extensive orbits: although others of them were of opinion, that the comets were only meteors raised very high in the air, which, blazing for a while, disappear when the matter of which they consist is consumed or dispersed. The branch of dialling was also practised among them long before the Greeks were acquainted with that science.

The Egyptians, it appears from various circumstances, were much of the same standing in Astronomy as the Chaldeans. Herodotus ascribes their knowledge in the science to Sesostris; probably not the same whom Newton makes contemporary with Solomon, as they were acquainted with astronomy at least many hundred years before that æra. We learn, from the testimony of some ancient authors, many particulars relative to the state of their knowledge in astronomy; such as, that they believed the figure of the earth was spherical; that the moon was eclipsed by passing through the earth's shadow, though it does not certainly appear that they had any knowledge of the true system of the universe; that they attempted to measure the magnitude of the earth and sun, though their methods of ascertaining the latter were very erroneous; and that they even pretended to foretel the appearance of comets, as well as earthquakes and inundations; and the same is also asscribed to the Chaldeans; though these must probably have been rather a kind of astrological predictions, than observations drawn from astronomy, properly so called.

This science however fell into great decay with the Egyptians, and in the time of the emperor Augustus, it was entirely extinct among them.

From Chaldea and Egypt the science of astronomy passed into Phenicia, which this people applied to the purposes of navigation, steering their course by the north polar star; and hence they became masters of the sea, and of almost all the commerce in the world. |

The Greeks, it is probable, derived their astronomical knowledge chiefly from the Egyptians and Phenicians, by means of several of their countrymen whovisited these nations, for the purpose of learning the different sciences. Newton supposes that most of the constellations were invented about the time of the Argonautic expedition; but it is more probable that they were, at least most part of them, of a much older date, and derived from other nations, though cloathed in fables of their own invention or application. Several of the constellations are mentioned by Hesiod and Homer, the two most ancient writers among the Greeks, and who lived about 870 years before Christ. Their knowledge in this science however was greatly improved by Thales the Milesian, and other Greeks, who travelled into Egypt, and brought from thence the chief principles of the science. Thales was born about 640 years before Christ; and he, first of all among the Greeks, observed the stars, the solstices, the eclipses of the sun and moon, and predicted the same. And the same was farther cultivated and extended by his successors Anaximander, Anaximanes, and Anaxagoras; but most especially by Pythagoras, who was born 577 years before Christ, and having resided for several years in Egypt, &c, brought from thence the learning of these people, taught the same in Greece and Italy, and founded the sect of the Pythagoreans. He taught that the sun was in the centre of the universe; that the earth was round, and people had antipodes; that the moon reflected the rays of the sun, and was inhabited like the earth; that comets were a kind of wandering stars, disappearing in the further parts of their orbits; that the white colour of the milky-way was owing to the united brightness of a great multitude of small stars; and he supposed that the distances of the moon and planets from the earth, were in certain harmonic proportions to one another.

Philolaus, a Pythagorean, who flourished about 450 years before Christ, asserted the annual motion of the earth about the sun; and not long after, the diurnal motion of the earth on her own axis, was taught by Hicetas, a Syracusan. About the same time flourished at Athens, Meton and Euctemon, where they observed the summer solstice 432 years before Christ, and observed the risings and settings of the stars, and what seasons they answered to. Meton also invented the cycle of 19 years, which still bears his name.

Eudoxus the Cnidian lived about 370 years before Christ, and was accounted one of the most skilful astronomers and geometricians of antiquity, being accounted the inventor of many of the propositions in Euclid's Elements, and having introduced geometry into the science of astronomy. He travelled into Asia, Africa, Sicily, and Italy, for improvements in astronomy; and we are informed by Pliny, that he determined the annual year to contain 365 days 6 hours, that he determined also the periodical times of the planets, and made other important observations and discoveries.

Calippus flourished foon after Eudoxus, and his celestial sphere is mentioned by Aristotle; but he is better known by a period of 76 which he invented, containing 4 corrected Metonic periods, and which commenced at the summer solstice in the year 330 before Christ. About his time the knowledge of the Pythagorean system was carried into Italy, Gaul, and Egypt, by certain colonies of Greeks.

However, the introduction of Astronomy into Greece is represented by Vitruvius in a manner somewhat different. He maintains, that Berosus, a Babylonian, brought it immediately from Babylon itself, and opened an astronomical school in the isle of Cos. And Pliny says, that in consideration of his wonderful predictions, the Athenians erected him a statue in the gymnasium, with a gilded tongue. But if this Berosus be the same with the author of the Chaldaic histories, he must have lived before Alexander.

After the death of this conqueror, the sciences flourished chiesly in Egypt, under the auspices of Ptolemy Philadelphus and his successors. He founded a school there, which continued to be the grand feminary of learning, till the invasion of the Saracens in the year of Christ 650. From the founding of that school, the science of astronomy advanced considerably. Aristarchus, about 270 years before Christ, strenuously asserted the Pythagorean system, and gave a method of determining the sun's distance by the dichotomy of the moon.—Eratosthenes, who was born at Cyrene in the year 27<*> before Christ, measured the circumference of the earth by means of a gnomon; and being invited to Alexandria, from Athens, by Ptolemy Euergetes, and made keeper of the royal library there, he set up for that Prince those armillary spheres, which Hipparchus and Ptolemy the astronomer afterwards employed so successfully in observing the heavens. He also determined the distance between the tropicsto be 11/83 of the whole meridian circle, which makes the obliquity of the ecliptic in his time to be 23° 51′ 1/3.— The celebrated Archimedes, too, cultivated astronomy, as well as geometry and mechanics: he determined the distances of the planets from one another, and constructed a kind of planetarium or orrery, to represent the phenomena and motions of the heavenly bodies.

To pass by several others of the ancients, who practised or cultivated astronomy, more or less, we find that Hipparchus, who flourished about 140 years before Christ, was the first who applied himself to the study of every part of astronomy, and, as we are informed by Ptolemy, made great improvements in it: he discovered that the orbits of the planets are eccentric, that the moon moved slower in the apogee than in her perigee, and, that there was a motion of anticipation of the moon's nodes: he constructed tables of the motions of the sun and moon, collected accounts of such eclipses, &c, as had been made by the Egyptians and Chaldeans, and calculated all that were to happen for 600 years to come: he discovered that the fixed stars changed their places, having a slow motion of their own from west to east: he corrected the Calippic period, and pointed out some errors in the method of Eratosthenes for measuring the circumference of the earth: he computed the sun's distance more accurately than any of his predecessors: but his chief work is a catalogue which he made of the fixed stars, to the number of 1022, with their longitudes, latitudes, and apparent magnitudes; which, with most of his other observations, are preserved by Ptolemy in his Almagest.

There was but little progress made in astronomy from the time of Hipparchus to that of Ptolemy, who was | born at Pelusium in Egypt, in the first century of christianity, and who made the greatest part of his observations at the celebrated school of Alexandria in that country. Prositing of those of Hipparchus and other ancient astronomers, he formed a system of his own, which, though erroneous, was followed for many ages by all nations. He compiled a great work, called the Almagest, which contained the observations and collections of Hipparchus and others his predecessors in astronomy, on which account it will ever be valuable to the professors of that science. This work was preserved from the grievous conflagration of the Alexandrine library by the Saracens, and translated out of Greek into Arabic in the year 827, and from thence into Latin in 1230. The Greek original was not known in Europe till the beginning of the 15th century, when it was brought from Constantinople, then taken by the Turks, by George, a monk of Trapezond, by whom it was translated into Latin; and various other editions have been since made.

During the long period from the year 800 till the beginning of the 14th century, the western parts of Europe were immersed in gross ignorance and barbarity, while the Arabians, profiting by the books they had preserved from the wreck of the Alexandrine library, cultivated and improved all the sciences, and particularly that of astronomy, in which they had many able professors and authors. The caliph Al Mansur first introduced a taste for the sciences into his empire. His grandson Al Mamun, who ascended the throne in 814, was a great encourager and improver of the sciences, and especially of astronomy. Having constructed proper ininstruments, he made many observations; determined the obliquity of the ecliptic to be 23° 35′; and under his auspices a degree of the circle of the earth was measured a second time in the plain of Singar, on the border of the Red Sea. About the same time Alferganus wrote elements of astronomy; and the science was from hence greatly cultivated by the Arabians, but principally by Albategnius, who flourished about the year 880, and who greatly reformed astronomy, by comparing his own observations with those of Ptolemy: hence he computed the motion of the sun's apogee from Ptolemy's time to his own; settled the precession of the equinoxes at one degree in 70 years; and fixed the obliquity of the ecliptic at 23° 35′. The tables which he composed, for the meridian of Aracta, were long esteemed by the Arabians. After his time, though the Saracens had many eminent astronomers, several centuries elapsed without producing any very valuable observations, excepting those of some eclipses observed by Ebn Younis, astronomer to the caliph of Egypt, by means of which the quantity of the moon's acceleration since that time may be determined.

Other eminent Arabic astronomers, were, Arzachel a Moor of Spain, who observed the obliquity of the ecliptic: he also improved Trigonometry by constructing tables of sines, instead of chords of arches, dividing the diameter into 300 equal parts. And Alhazen, his contemporary, who wrote upon the twilight, the height of the clouds, the phenomenon of the horizontal moon, and who first shewed the importance of the theory of refractions in astronomy.

Ulug Beg, grandson of the celebrated Tartar prince Tamerlane, was a great proficient in practical astronomy; he had very large instruments, particularly a quadrant of about 180 feet high, with which he made good observations. From these he determined the latitude of Samercand, his capital, to be 39° 37′ 23″; and com posed astronomical tables for the meridian of the same so exact, that they differ very little from those constructed afterwards by Tycho Brahe; but his principal work was his catalogue of the fixed stars, made also from his own observations in the year 1437.

During this period, almost all Europe was immersed in gross ignorance. But the settlement of the Moors in Spain introduced the sciences into Europe; from which time they have continued to improve, and to be communicated from one people to another, to the present time, when astronomy and all the sciences, have arrived at a very eminent degree of perfection. The emperor Frederick II, about 1230, first began to encourage learning; restoring some decayed universities, and founding a new one in Vienna: he also caused the works of Aristotle, and Ptolemy's Almagest, to be translated into Latin; and from the translation of this work we may date the revival of astronomy in Europe. Two years after this, John de Sacro Bosco, that is, of Halifax, compiled, from Ptolemy, Albategnius, Alferganus, and other Arabic astronomers, his work De Sphæra, which was held in the greatest estimation for 300 years after, and was honoured with commentaries by Clavius and other learned men. In 1240, Alphonso, king of Castile, not only cultivated astronomy himself, but greatly encouraged others; and by the assistance of several learned men he corrected the tables of Ptolemy, and composed those which were denominated from him the Alphonsine Tables. About the same time also, Roger Bacon, an English monk, wrote several tracts relative to astronomy, particularly of the lunar aspects, the solar rays, and the places of the fixed stars. And, about the year 1270, Vitello, a Polander, composed a treatise on optics, in which he shewed the use of refractions in astronomy.

Little other improvement was made in astronomy till the time of Purbach, who was born in 1423. He composed new tables of sines for every 10 minutes, making the radius 60, with four ciphers annexed. He constructed spheres and globes, and wrote several astronomical tracts; as, a commentary on Ptolemy's Almagest; some treatises on Arithmetic and Dialling, with tables for various climates; new tables of the fixed stars reduced to the middle of that century; and he corrected the tables of the planets, making new equations to them where the Alphonsine tables were erroneous. In his solar tables, he placed the sun's apogee in the beginning of Cancer; but retained the obliquity of the ecliptic 23° 33 1/2′, as determined by the latest observations. He also observed some eclipses, made new tables for computing them, and had just finished a theory of the planets, when he died in 1462, being only 39 years of age.

Purbach was succeeded in his astronomical and mathematical labours by his pupil and friend, John Muller, commonly called Regiomontanus, from Monteregio, or Koningsberg, a town of Franconia, where he was born. He completed the epitome of Ptolemy's Almagest, which Purbach had begun; and after the death of his friend, was invited to Rome, where he made many | astronomical observations. Being returned to Nuremberg in 1471, by the encouragement of a wealthy citizen named Bernard Walther, he made several instruments for astronomical observations, among which was an armillary astrolabe, like that used at Alexandria by Hipparchus and Ptolemy, with which he made many observations, using also a good clock, which was then but a late invention. He made ephemerides for 30 years to come, shewing the lunations, eclipses, &c; and, the art of printing having then been lately invented, he printed the works of many of the most celebrated ancient astronomers. He wrote the Theory of the Planets and Comets, and a treatise on triangles, still in repute for several good theorems; computing the table of sines for every single minute, to the radius 1000000, and introducing the use of tangents also into trigonometry. After his death, which happened at Rome in 1476, being only 40 years of age, Walther collected his papers, and continued the astronomical observations till his own death also. The observations of both were collected by order of the senate of Nuremberg, and published there in 1544 by John Schoner: they were also afterwards published in 1618 by Snellius, at the end of the observations made by the Landgrave of Hesse; and lastly with those of Tycho Brahe in 1666.

Walther was succeeded, as astronomer at Nuremberg, by John Werner, a clergyman. He observed the motion of the comet in 1500; and wrote several tracts on geometry, astronomy, and geography, in a masterly manner; the most remarkable of which, are those concerning the motion of the 8th sphere, or of the fixed stars; in this tract, by comparing his own observations, made in 1514, with those of Ptolemy, Alphonsus, and others, he shewed that the motion of the fixed stars, since called the precession of the equinoxes, is 1° 10′ in 100 years. He made also the first star of Aries 26° distant from the equinoctial point, and the obliquity of the ecliptic only 23° 28′. He constructed a planetarium, representing the celestial motions according to the Ptolemaic hypothesis; and he published a translation of Ptolemy's Geography, with a commentary, in which he first proposed the method of finding the longitude at sea by observing the moon's distance from the fixed stars; now so successfully practised for that purpose. Werner died in 1528, at 60 years of age.

Nicolaus Copernicus was the next who made any considerable figure in astronomy, by whom indeed the old Pythagorean system of the world was restored, which had been till now set aside from the time of Ptolemy. About the year 1507 Copernicus conceived doubts of this system, and entertained notions about the true one, which he gradually improved by a series of astronomical observations, and the contemplation of former authors. By these he formed new tables, and completed his work in the year 1530, containing these, and his renovation of the true system of the universe, in which all the planets are considered as revolving about the sun, placed in the centre. But the work was only printed in 1543, underthe care of Schoner and Osiander, by the title of Revolutiones Orbium Cœlestium; and the author just received a copy of the work a few hours before his death, which happened on the 23d of May 1543, at 70 years of age.

After the death of Copernicus, the science and practice of astronomy were greatly improved by many other persons, as Schoner, Nonius, Appian, Gemma Frisius, Rothman, Byrgius, the Landgrave of Hesse, &c.— Schoner reformed and explained the calendar, improved the methods of making celestial observations, and published a treatise on cosmography; but he died 4 years after Copernicus.—Nonius wrote several works on mathematics, astronomy and navigation, and invented some useful and more accurate instruments than formerly; one of these was the astronomical quadrant, on which he divided the degrees into minutes by a number of concentric circles; the first of which was divided in 90 equal parts or degrees, the second into 89, the thirdinto 88, and so on, to 46; so that, the index of the quadrant always falling upon or near one of the divisions, the minutes would be known by an easy computation.—The chief work of Appian, The Cæsarean Astronomy, was published at Ingoldstat in 1540; in which he shews, how to observethe places of the stars and planets by the astrolabe; to resolve astronomical problems by certain instruments; to predict eclipses, and to describe the figures of them; and the method of dividing and using an astronomical quadrant: at the end are added observations of 5 comets, one of which has been supposed the same with that observed by Hevelius, and if so, it ought to have returned again in the year 1789;—but it was not observed then. Gemma Frisius wrote a commentary on Appian's Cosmography, accompanied with many observations of eclipses: he also invented the astronomical ring, and several other instruments, useful in taking observations at sea; and he was the first who recommended a timekeeper for determining the longitude at sea.—Rheticus gave up his professorship of mathematics at Wittemberg, that he might attend the astronomical lectures of Copernicus; and, for improving astronomical calculations, he began a very extensive work, being a table of sines, tangents and secants, to a very large radius, and to every 10 seconds, or 1/6 of a minute; which was completed by his pupil Valentine Otho, and published in 1594.

About the year 1561, William IV, Landgrave of Hesse Cassel, applied himself to the study of astronomy, having furnished himself with the best instruments that could then be made: with these he made a great number of observations, which were published by Snellius in 1618, and which were preferred by Hevelius to those of Tycho Brahe. From these observations he formed a catalogue of 400 stars, with their latitudes and longitudes, adapted to the beginning of the year 1593.

Tycho Brahe, a noble Dane, began his observations about the same time with the Landgrave of Hesse, abovementioned, and he observed the great conjunction of Jupiter and Saturn: but finding the usual instruments very inaccurate, he constructed many others much larger and exacter, with which he applied himself diligently to observe the celestial phenomena. In 1571 he discovered a new star in the chair of Cassiopeia; which induced him, like Hipparchus on a similar occasion, to make a new catalogue of the stars; which he composed to the number of 777, and adapted their places to the year 1600. In the year 1576, by favour of the king of Denmark, he built his new observatory, called Uraniburg, on the small island Huenna, opposite | to Copenhagen, and which he very amply furnished with many large instruments, some of them so divided as to shew single minutes, and in others the arch might be read off to 10 seconds. One quadrant was divided according to the method invented by Nonius, that is, by 47 concentric circles; but most of them were divided by diagonals; a method of division invented by a Mr. Richard Chanceler, an Englishman. Tycho employed his time at Uraniburg to the best advantage, till the death of the king, when, falling into discredit, he was obliged to remove to Holstein; and he afterwards found means of introducing himself to the Emperor Rodolph, with whom he continued at Prague till the time of his death in 1601.—It is well known that Tycho was the inventor of a system of astronomy, a kind of Semi-PtoIemaic, which he vainly endeavoured to establish instead of the Copernican or true system. His works, however, which are very numerous, shew that he was a man of great abilities; and his discoveries, together with those of Purbach and Regiomontanus, were collected and published together in 1621, by Longomontanus, the favourite disciple of Tycho.

While Tycho resided at Prague with the emperor, he prevailed on Kepler to leave the university of Glatz, and to come to him, which he did with his family and library in 1600: but Tycho dying in 1601, Kepler enjoyed all his life the title of mathematician to the Emperor, who ordered him to sinish the tables of Tycho Brahe, which he did accordingly, and published them in 1627, under the title of Rodolphine. He died about the year 1630 at Ratisbon, where he was soliciting the arrears of his pension. From his own observations, and those of Tycho, Kepler discovered several of the true laws of nature, by which the motions of the celestial bodies are regulated. He discovered that all the planets revolved about the sun, not in circular, but in elliptical orbits, having the sun in one of the foci of the ellipse; that their motions were not equable, but varying, quicker or slower as they were near to the sun or farther from him; but that this motion was so regulated, that the areas described by the variable line drawn from the planet to the sun, are equal in equal times, and always proportional to the times of describing them. He also discovered, by trials, that the cubes of the distances of the planets from the sun, were in the same proportion as the squares of their periodical times of revolution. By observations also on comets, he concluded that they are freely carried about among the orbits of the planets, in paths that are nearly rectilinear, but which he could not then determine. Besides many other discoveries, which are to be found in his writings.

In Kepler's time there were many other good prosicients in astronomy; as Edward Wright, baron Napier, John Bayer, &c. Wright made several good meridional observations of the sun, with a quadrant of 6 feet radius, in the years 1594, 1595, and 1596; from which he greatly improved the theory of the sun's motion, and computed more accurately his declination, than any person had done besore. In 1599 he published also an excellent work entitled “Certain Errors in Navigation discovered and detected,” containing a method which has commonly, though erroneously, been ascribed to Mercator.—To Napier we owe some excellent theorems and improvements in spherics, besides the ever memo- rable invention of logarithms, one of the most usefut ever made in the art of numbering, and of the greatest use in all the other mathematical sciences.—Bayer, a German, published his Uranometria, being a complete celestial atlas, or the figures of all the constellations visible in Europe, with the stars marked on them, and the stars also accompanied by names, or the letters of the Greek alphabet; a contrivance by which the stars may easily be referred to with distinctness and precision. —About the same time too, astronomy was cultivated by many other persons; namely, abroad by Mercator, Maurolycus, Maginus, Homelius, Schultet, Stevin, Galileo, &c; and in England by Thomas and Leonard Digges, John Dee, Robert Flood, Harriot, &c.

The beginning of the 17th century was particularly distinguished by the invention of telescopes, and the application of them to astronomical observations; an invention to which we owe the most brilliant discoveries, and all the accuracy to which the science is now brought. The more distinguished early observations with the telescope, were made by Galileo, Harriot, Huygens, Hook, Cassini, &c. It is said that from report only, and before he had seen one, Galileo made for himself telescopes, by which he discovered inequalities in the moon's surface, Jupiter's satellites, and the ring of Saturn; also spots on the sun, by which he found out the revolution of that luminary on his axis; and he discovered that the nebulæ and milky way were full of small stars. Harriot also, who has hitherto been known only as an algebraist, made much the same discoveries as Galileo, and as early, if not more so, as appears by his papers not yet printed, in the possession of the earl of Egremont.

Mr. Horrox, a young astronomer of great talents, made considerable discoveries and improvements. In 1633 he found out that the planet Venus would pass over the sun's disc on the 24th of November, 1639; an event which he announced only to his friend Mr. Crabtree; and these two were the only persons in the world that observed this transit, which was also the first time it had ever been seen by mortal eyes. Mr. Horrox made also many other useful observations, and had even formed a new theory of the moon, taken notice of by Newton; but his early death, in the beginning of the year 1640, put a slop to his useful and valuable labours.

About the same time flourished Hevelius, Burgomaster of Dantzic, who furnished an excellent observatory in his own house, where he observed the spots and phases of the moon, from which observations he compiled his Selenographia; and an account of his apparatus is contained in his work entitled Machina Cœlestis, a book now very scarce, as most of the copies were accidentally burnt, with the whole house and apparatus, in 1679. Hevelius died in 1688, aged 76.

Dr. Hook, a contemporary of Hevelius, invented instruments with telescopic sights, and censured those of the latter; which occasioned a sharp dispute between them, and to settle which the celebrated Dr. Halley was sent over to Hevelius to examine his instruments. The two astronomers made several observations together, very much to their satisfaction, and amongst them was one of an occultation of Jupiter by the moon, when they determined the diameter of the latter to be 30′ 33.″ |

Before the middle of the 17th century the construction of telescopes had been greatly improved, particularly by Huygens and Fontana. The former constructed one of 123 feet, with which he long observed the moon and planets, and discovered that Saturn was encompassed with a ring. With telescopes too, of 200 and 300 feet focus, Cassini saw five satellites of Saturn, with his zones or belts, and the shadows of Jupiter's satellites passing over his body. In 1666 Azout applied a micrometer to telescopes, to measure the diameters of the planets, and other small distances in the heavens: but an instrument of this kind had been invented before, by Mr. Gascoigne, though it was but little known abroad.

To obviate the difficulties of the great lengths of refracting telescopes and the aberration of the rays, it is said that Mersennus first started the idea of making telescopes of reflectors, instead of lenses, in a letter to Descartes; and in 1663 James Gregory of Aberdeen shewed how such a telescope might be constructed. After some time spent also by Newton, on the construction of both sorts of telescopes, he found out the great inconvenience which arises to refractors from the different refrangibility of the rays of light, for which he could not then find a remedy; and therefore, pursuing the other kind, in the year 1672 he presented to the Royal Society two reflectors, which were constructed with spherical speculums, as he could not procure other figures. The inconveniences however arising from the different refrangibility of the rays of light, have since been fully obviated by the ingenious Mr. Dollond. Towards the latter part of the 17th, and beginning of the 18th century, practical altronomy it seems rather languished. But at the same time the speculative part was carried to the highest perfection by the immortal Newton in his Principia, and by the Astronomy of David Gregory.

Soon after this however, great improvements of astronomical instruments began to take place, particularly in Britain. Mr. Graham, a celebrated mechanic and watchmaker, not only improved clocks and watch work, but also carried the accuracy of astronomical instruments to a surprising degree. He constructed the old 8 feet mural arch at the Royal Observatory Greenwich, and a small equatorial sector for making observations out of the meridian; but he is chiefly remarkable for contriving the zenith sector of 24 feet radius, and afterwards one of 12 1/2 feet, with which Dr. Bradley discovered the aberration of the fixed stars. The reflecting telescope of Gregory and Newton, was greatly improved by Mr. Hadley, who presented a very powerful instrument of that kind to the Royal Society in 1719. The same gentleman has also immortalized his memory by the invention of the reflecting quadrant or sector, now called by his name, which he presented to the society in 1731, and which is now so universally useful at sea, especially where nice observations are required. It appears however that an instrument similar to this in its principles, had been invented by Newton; and a description with a drawing of it given by him to Dr. Halley, when he was preparing for his voyage in 1701, to discover the variation of the needle: it has also been asserted that a Mr. Godfrey of Philadelphia in America, made the same discovery, and the first instrument of this kind. About the middle of this century, the constructing and dividing of large astronomical instruments were carried to great perfection by Mr. John Bird; and reflecting telescopes were not less improved by Mr. Short, who also first executed the divided object-glass micrometer, which had been proposed and described by M. Louville and others, Mr. Dollond also brought refracting telescopes to the greatest perfection, by means of his acromatic glasses; and lately the discoveries of Herschel are owing to the amazing powers of reflectors of his own construction.

Thus the astronomical improvements in the present century, have been chiefly owing to the foregoing inventions and improvements in the instruments, and to the establishment of regular observatories in England, France, and other parts of Europe. Roemer, a celebrated Danish Astronomer, first made use of a meridional telescope; and, by observing the eclipses of Jupiter's satellites, he first discovered the progressive motion of light, concerning which he read a differtation before the Academy of Sciences at Paris in 1675.—Mr. Flamsteed was appointed the first Astronomer Royal at Greenwich in 1675. He observed, for 44 years, all the celestial phenomena, the sun, moon, planets, and fixed stars, of all which he gave an improved theory and tables, viz, a catalogue of 3000 stars with their places, to the year 1689; also new solar tables, and a theory of the moon according to Horrox; likewise, in Sir Jonas Moore's System of Mathematics, he gave a curious tract on the doctrine of the sphere, shewing how, geometrically to construct eclipses of the sun and moon, as well as occultations of the fixed stars by the moon. And it was upon his tables that were constructed, both Halley's tables, and Newton's theory of the moon.—Cassini also, the first French Astronomer Royal, very much distinguished himself, making many observations on the sun, moon, planets and comets, and greatly improved the elements of their motions. He also erected the gnomon, and drew the celebrated meridian line in the church of Petronia at Bologna.

In 1719 Mr. Flamsteed was succeeded by Dr. Halley, as Astronomer Royal at Greenwich. The Doctor had been sent at the early age of 21 to the island of St. Helena, to observe the southern stars, and make a catalogue of them, which was published in 1679. In 1705 he published his Synopsis Astronomiæ Cometicæ, in which he ventured to predict the return of a comet in 1758 or 1759. He was the first who discovered the acceleration of the moon, and he gave a very ingenious method for finding her parallax by three observed phases of a solar eclipse. He published, in the Philosophical Transactions, many learned papers, and amongst them some that were concerning the use that might be made of the next transit of Venus in determining the distance of the sun from the earth. He composed tables of the sun, moon, and all the planets, which are still in great repute; with which he compared the observations he made of the moon at Greenwich, amounting to near 1500, and noted the differences. He recommended the method of determining the longitude by the moon's distances from the sun and certain fixed stars; a method which had before been noticed, and which has since been carried into execution, more particularly at the instance of the present Astronomer Royal.

About this time a dispute arose concerning the figure of the earth. Sir Isaac Newton had determined, from a consideration of the laws of gravity, and the diurnal motion of the earth, that the figure of it was an oblate | spheroid, and flatted at the poles: but Cassini had determined, from the measures of Picart, that the figure was an oblong spheroid, or lengthened at the poles. To settle this dispute, it was resolved, under Lewis XV, to measure two degrees of the meridian; one near the equator, and the other as near the pole as possible. For this purpose, the Royal Academy of Sciences sent to Lapland, Mess. Maupertuis, Clairault, Camus, and Le Monier; being also accompanied by the Abbé Outhier, and by M. Celsus, professor of anatomy at Upsal. And on the southern expedition were sent Mess. Godin, Condamine, and Bouguer, to whom the king of Spain joined Don George Juan and Don Antonio de Ulloa. These set out in 1735, and returned at different times in 1744, 1745, and 1746; but the former party, who set out only in 1736, returned the year following; having both fulfilled their commissions. Picart's measure was also revised by Cassini and De la Caille, which after his errors were corrected, was found to agree very well with the other two; and the result of the whole served to confirm the determination of the figure before laid down by Newton.—On the southern expedition, it was found that the attraction of the great mountains of Peru had a sensible effect on the plumb-line of one of their largest instruments, deflecting it 7 or 8 seconds from the true perpendicular.

On the death of Dr. Halley, in 1742, he was succeeded by Dr. Bradley, as Astronomer Royal at Greenwich. The accuracy of his observations enabled him to detect the smaller inequalities in the motions of the planets and fixed stars. The consequence of this accuracy was, the discovery of the aberration of light, the nutation of the earth's axis, and a much greater degree of perfection in the lunar tables. He also observed the places, and computed the elements of the comets which appeared in the years 1723, 1736, 1743, and 1757. He made new and accurate tables of the motions of Jupiter's satellites; and from a multitude of observations of the luminaries, he constructed the most accurate table of refractions yet extant. Also, with a very large transit instrument, and a new mural quadrant of 8 feet radius, constructed by Mr. Bird in 1750, he made an immense number of observations for settling the places of all the stars in the British catalogue, together with near 1500 places of the moon, the greater part of which he compared with Mayer's tables. Dr. Bradley died in 1762.

In the mean time the mathematicians and astronomers elsewhere were assidnous in their endeavours to promote the science of astronomy. The theory of the moon was particularly considered by Messrs Clairault, D'Alembert, Euler, Meyer, Simpson, and Walmsly, and especially Clairault, Euler, and Mayer, who computed complete sets of lunar tables; those of the last of these authors, for their superior accuracy, were rewarded with a premium of 3000 pounds by the Board of Longitude, who brought them into use in the computation of the Nautical Ephemeris, published by that Board.—The most accurate tables of the satellites of Jupiter were composed, from observations by Mr. Wargentin, an excellent Swedish astronomer.—Among the many French astronomers who contrib<*>ted to the advancement of the science, it was particalarly indebted to M. De la Caille, for an excellent set of solar tables. And in 1750 he went to the Cape of Good Hope to make observations in concert with the most celebrated astronomers in Europe, for determining the parallax of Mars and the moon, and thence, that of the sun, which it was concluded did not much exceed 10 seconds. Here he re-examined and adjusted, with great accuracy, the stars about the southern pole; and also measured a degree of the meridian. —In Italy the science was assiduously cultivated by Bianchini, Boscovich, Frisi, Manfredi, Zanotti, and many others; in Sweden by Wargentin already mentioned, Blingenstern, Mallet, and Planman; and in Germany by the Eulers, Mayer, Lambert, Grischow, and others.

In the year 1760 all the learned Societies in Europe made preparations for observing the transit of Venus over the sun, which had been predicted by Dr. Halley more than 80 years before, and the use that might be made of it in determining the sun's parallax, and the distances of the planets from the sun. And the same exertions were repeated, to observe the transit in 1769, by sending observers to different parts of the world, for the more convenience in observing. And from the whole, Mr. Short computed that the sun's parallax was nearly 8 3/5 seconds, and consequently the distance of the sun from the earth about 24114 of the earth's diameters, or 96 millions of miles.

Dr. Bradley was succeeded, in 1762, in his office of Astronomer Royal, by Mr. Bliss, Savilian professor of astronomy; who being in a declining state of health, did not long enjoy it. But, dying in 1765, was sueceeded by the learned Nevil Maskelyne, D. D. the present Astronomer Royal, who has discharged the duties of that office with the greatest honour to himself, and benesit to the science. In January 1761 this gentleman was sent by the Royal Society, at a very early age, to the Island of St. Helena, to observe the transit of Venus over the sun, and the parallax of the star Sirius. The sirst of these objects partly failed, by clouds preventing the sight of the 2d internal contact; and the 2d also, owing to Mr. Short having suspended the plumbline by a loop from the neck of the central pin. However, our astronomer indemnified himself by many other valuable observations: Thus, he observed at St. Helena, the tides; the horary parallaxes of the moon; and the going of a clock, to sind, by comparison with its previous going which had been observed in England, the difference of gravity at the two places: also, in going out and returning, he practised the method of finding the longitude by the lunar distances taken with a Hadley's Quadrant, making out rules for the use of seamen, and taught the method to the ossicers on board the ship; which he afterwards explained in a l<*>tter to the Secretary of the Royal Society, inserted in the Philos. Trans. sor the year 1762, and still more fully afterwards, in the British Mariner's Guide, which he published in the year 1763. He returned from St. Helena in the spring of 1762, after a stay there of 10 months; and in September 1763 sailed for the island of Barbadoes, to settle the longitude of the place, and to compare Mr. Harrison's watch with the time there when this gentleman should bring it out: another object was also to try Mr. Irwin's marine chair, which he did in his way out. While at Barbadoes, he also made many other observations, and amongst them, many relating to the moon's horary parallaxes, not yet published. Returning to England in the latter part of the year 1764, he was | appointed in 1765 to succeed Mr. Bliss as Astronomer Royal, and immediately recommended to the Board of Longitude the lunar method of finding the longitude, and proposed to them the project of a Nautical Almanac, to be calculated and published to facilitate that method; this they agreed to, and the first vol. was published for 1767, and it has continued ever since under his direction, to the great benefit of navigation and universal commerce.

A multitude of other useful writings by this gentleman are inserted in the volumes of the Philos. Trans. and particularly in consequence of a proposal, made by him to the Royal Society, the noble project was formed of measuring very accurately the effect of some mountain on the plumb line, in deflecting it from the perpendicular; and the mountain of Schehallien, in Scotland, having been found the most convenient in this island for the purpose, at the request of the Society, he went into Scotland to conduct the business, which he performed in the most accurate manner, shewing that the sum of the deflections on the two opposite sides was about 11 3/5 seconds of a degree; and proving, to the satisfaction of the whole world, the universal attraction of all matter. From the data resulting from these measures I have computed the mean density of the whole matter in the earth, which I have found to be about 4 1/2 times that of common water. Besides many learned and valuable papers in the Philosophical Transactions, and the most assiduous exertions in the duties of the observatory, as abundantly appears by the curious and voluminous observations which he has published, the world is particularly obliged to his endeavours with the Board of Longitude, for the publication of the Nautical Ephemeris, and the method of observing the longitude, by the distances of the moon and stars, now adopted by all nations, and by which the practice of Navigation has been brought to the greatest perfection.

Finally, the discoveries of Dr. Herschel form a new æra in astronomy. He first, in 1781, began with observations on the periodical star in Collo Ceti, and a new method of measuring the lunar mountains, none of which he made more than half <*> mile in height: and, having constructed telescopes vastly more powerful than any former ones, he proceeded to other observations, concerning which he has had several papers printed in the Philosophical Transactions; as, on the rotation of the planets round their axes; On the parallax of the fixed stars; Catalogues of double, triple, &c stars; On the proper motion of the sun and solar system; On the remarkable appearances of the solar regions of the planet Mars, &c. And, above all, his discovery of a new primary planet, on the 13th of March 1781, which he calls the Georgian Planet, but it is named the Planet Herschel by the French and other foreign astronomers; by which, and its two satellites, which he has also discovered since that time, he has greatly enlarged the bounds of the solar system, this new planet being more than twice as far from the sun as the planet Saturn.

Lists and historical accounts of the principal writings and authors on astronomy are contained in Weidler's History of Astronomy, which is brought down to the year 1737. There is also Bailly's History of astronomy, ancient and modern. For this purpose, consult also the following authors, viz, Adam, Vossius, Bayle, Chauffepié, Niceron, Perraut, the chronological table of Riccioli, and that of Sherburn, at the end of his edition of Manilius; also the first volume of De la Lande's astronomy. The more modern, and popular books on astronomy, are very numerous, and well known: as those of Ferguson, Long, Emerson, Vince, De la Lande, Leadbetter, Brent, Keil, Whiston, Wing, Street, &c, &c.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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