They determined the circ.u.mference of the earth by a method identical with that which would be employed by modern astronomers. They ascertained the position of the stars by right ascension and declination. They knew the obliquity of the ecliptic, and determined the place of the sun's apogee as well as its mean motion. Their calculations on the eccentricity of the moon prove that they had a rectilinear trigonometry and tables of chords. They had an approximate knowledge of parallax. [Footnote: Delambre, _Hist. d'Astr. Anc._, tom. 1, p.

184.] They could calculate eclipses of the moon, and use them for the correction of their lunar tables. They understood spherical trigonometry, and determined the motions of the sun and moon, involving an accurate definition of the year, and a method of predicting eclipses.

They ascertained that the earth was a sphere, and reduced the phenomena of the heavenly bodies to uniform movements of circular orbits.

[Footnote: Lewis, _Hist. of Astron._, p. 209.] We have settled, by physical geography, the exact form of the earth, but the ancients arrived at their knowledge by astronomical reasoning. "The reduction of the motions of the sun, moon, and five planets to circular orbits, as was done by Hipparchus, implies deep concentrated thought and scientific abstraction. The theory of eccentrics and epicycles accomplished the end of explaining all the known phenomena. The resolution of the apparent motions of the heavenly bodies into an a.s.semblage of circular motions, was a great triumph of genius, [Footnote: Whewell, _Hist. Induc.

Science_, v. i. p. 181.] and was equivalent to the most recent and improved processes by which modern astronomers deal with such motions."

But I will not here enumerate the few discoveries which were made by the Alexandrian school. I only wish to show that there are a few names among the ancients which are inscribed on the roll of great astronomers, limited as were the triumphs of the science itself. But, until the time of Aristarchus, most of the speculations were crude and useless. Nothing can be more puerile than the notions of the ancients respecting the nature and motions of the heavenly bodies.

[Sidenote: Astronomy born in Chaldea.]

Astronomy was probably born in Chaldea as early as the time of Abraham.

The glories of the firmament were impressed upon the minds of the rude primitive races with an intensity which we do not feel with all the triumphs of modern science. The Chaldean shepherds, as they watched their flocks by night, noted the movements of the planets, and gave names to the more brilliant constellations. Before religious rituals were established, before great superst.i.tions arose, before poetry was sung, before musical instruments were invented, before artists sculptured marble or melted bronze, before coins were stamped, before temples arose, before diseases were healed by the arts of medicine, before commerce was known, before heroes were born, those oriental shepherds counted the hours of anxiety by the position of certain constellations. Astronomy is, therefore, the oldest of the ancient sciences, although it remained imperfect for more than four thousand years. The old a.s.syrians, Egyptians, and Greeks made but few discoveries which are valued by modern astronomers, but they laid the foundation of the science, and ever regarded it as one of the n.o.blest subjects which could stimulate the faculties of man. It was invested with all that was religious and poetical.

[Sidenote: Discoveries made by oriental nations.]

The s.p.a.cious level and unclouded horizon of Chaldea afforded peculiar facilities of observation; and its pastoral and contemplative inhabitants, uncontaminated by the vices and superst.i.tions of subsequent ages, active-minded and fresh, discovered, after a long observation of eclipses--some say extending over nineteen centuries--the cycle of two hundred and twenty-three lunations, which brings back the eclipses in the same order. Having once established their cycle, they laid the foundation for the most sublime of all the sciences. Callisthenes transmitted from Babylon to Aristotle a collection of observations of all the eclipses that preceded the conquests of Alexander, together with the definite knowledge which the Chaldeans had collected about the motions of the heavenly bodies. It was rude and simple, and amounted to little beyond the fact that there were spherical revolutions about an inclined axis, and that the poles pointed always to particular stars.

The Egyptians also recorded their observations, from which it would appear that they observed eclipses at least one thousand six hundred years before the commencement of our era. Nor is this improbable, if the speculations of modern philosophers respecting the age of the world are ent.i.tled to respect. The Egyptians discovered, by the rising of Sirius, that the year consists of three hundred and sixty-five and one quarter days, and this was their sacred year, in distinction from the civil, which consisted of three hundred and sixty-five days. They also had observed the courses of the planets, and could explain the phenomena of the stations and retrogradations, and it is even a.s.serted that they regarded Mercury and Venus as satellites of the sun. Some have maintained that the obelisks which they erected served the purpose of gnomons, for determining the obliquity of the ecliptic, the alt.i.tude of the pole, and the length of the tropical year. It is thought that even the Pyramids, by the position of their sides toward the cardinal points, attest their acquaintance with a meridional line. The Chinese boast of having noticed and recorded a series of eclipses extending over a period of three thousand eight hundred and fifty-eight years, and it is probable that they antic.i.p.ated the Greeks two thousand years in the discovery of the Metonic cycle, or the cycle of nineteen years, at the end of which time the new moons fall on the same days of the year. They determined the obliquity of the ecliptic, one thousand one hundred years before our era, to be 23 degrees 54' 3-15". The Indians, at a remote antiquity, represented celestial phenomena with considerable exactness, and constructed tables by which the longitude of the sun and moon are determined. Bailly thinks that astronomy was cultivated in Siam three thousand one hundred and two years before Christ, which hardly yields in accuracy to that which modern science has built on the theory of universal gravitation. The Greeks divided the heavens into constellations fourteen centuries before Christ. Thales, born 640 B.C., taught the rotundity of the earth, and that the moon shines with reflected light. He also predicted eclipses. Anaximander, born 610 B.C., invented the gnomon, and constructed geographical charts.

[Sidenote: The early Greek investigators.]

But the Greeks, after all, were the only people of antiquity who elevated astronomy to the dignity of a science. They however confessed that they derived their earliest knowledge from the Babylonian and Egyptian priests, while the priests of Thebes a.s.serted that they were the originators of exact astronomical observations. [Footnote: Diod., i.

50.] Diodorus a.s.serts that the Chaldeans used the Temple of Belus, in the centre of Babylon, for their survey of the heavens. [Footnote: Diod., ii. 9.] But whether the Babylonians or the Egyptians were the earliest astronomers, it is of little consequence, although the pedants make it a grave matter of investigation. All we know is, that astronomy was cultivated by both Babylonians and Egyptians, and that they made but very limited attainments. The early Greek philosophers, who visited Egypt and the East in search of knowledge, found very little to reward their curiosity or industry; not much beyond preposterous claims to a high antiquity, and an esoteric wisdom which has not yet been revealed.

They approximated to the truth in reference to the solar year, by observing the equinoxes and solstices, and the heliacal rising of particular stars. Plato and Eudoxus spent thirteen years in Heliopolis for the purpose of extracting the scientific knowledge of the priests, but they learned but little beyond the fact that the solar year was a trifle beyond three hundred and sixty-five days. No great names have come down to us from the priests of Babylon or Egypt. No one gained an individual reputation. The Chaldean and Egyptian priests may have furnished the raw material of observation to the Greeks, but the latter alone possessed the scientific genius by which indigested facts were converted into a symmetrical system. The East never gave valuable knowledge to the West. It gave only superst.i.tion. Instead of astronomy, it gave astrology; instead of science, it gave magic and incantations and dreams--poison which perverted the intellect. [Footnote: Sir G. G.

Lewis, _Hist. of Anc. Astron._, p. 293.] They connected their astronomy with divination from the stars, and made their antiquity reach back to two hundred and seventy thousand years. There were soothsayers in the time of Daniel, and magicians, exorcists, and interpreters of signs. [Footnote: Dan. i. 4, 17, 20.] They were not men of scientific research, seeking truth. It was power they sought, by perverting the intellect of the people. The astrology of the East was founded on the principle that a star or constellation presided over the birth of an individual, and either portended his fate, or shed a good or bad influence upon his future life. The star which looked upon a child at the hour of his birth, was called the horoscopus, and the peculiar influence of each planet was determined by professors of the genethliac art. The superst.i.tions of Egypt and Chaldea unfortunately spread both among the Greeks and Romans, and these were about all that the western nations learned from the boastful priests of occult science. Whatever was known of real value among the ancients, is due to the earnest inquiries of the Greeks.

[Sidenote: Researches of the Greeks.]

And yet their researches were very unsatisfactory until the time of Hipparchus. The primitive knowledge, until Thales, was almost nothing.

The Homeric poems regarded the earth as a circular plain, bounded by the heaven, which was a solid vault or hemisphere, with its concavity turned downwards. And this absurdity was believed until the time of Herodotus, five centuries after; nor was it exploded fully in the time of Aristotle. The sun, moon, and stars, were supposed to move upon, or with, the inner surface of the heavenly hemisphere, and the ocean was thought to gird the earth around as a great belt, into which the heavenly bodies sunk at their setting. [Footnote: _Il_., vii. 422; _Od_., iii. i. xix. 433.] Homer believed that the sun arose out of the ocean, ascending the heaven, and again plunging into the ocean, pa.s.sing under the earth, and producing darkness. [Footnote: _Il_.

viii. 485.] The Greeks even personified the sun as a divine charioteer driving his fiery steeds over the steep of heaven, until he bathed them at evening in the western waves. Apollo became the G.o.d of the sun, as Diana was the G.o.ddess of the moon. But the early Greek inquirers did not attempt to explain how the sun found his way from the west back again to the east. They merely took note of the diurnal course, the alternation of day and night, the number of the seasons, and their regular successions. They found the points of the compa.s.s by determining the recurrence of the equinoxes and solstices; but they had no conception of the ecliptic--of that great circle in the heaven, formed by the sun's annual course, and of its obliquity when compared with the equator. Like the Egyptians and Babylonians, they ascertained the length of the year to be three hundred and sixty-five days; but perfect accuracy was wanting for want of scientific instruments, and of recorded observations of the heavenly bodies. The Greeks had not even a common chronological era for the designation of years. Thus Herodotus informs us that the Trojan War preceded his time by eight hundred years: [Footnote: _Il_, ii. 53.] he merely states the interval between the event in question and his own time; he had certain data for distant periods. Thus the Greeks reckoned dates from the Trojan War, and the Romans from the building of their city. And they divided the year into twelve months, and introduced the intercalary circle of eight years, although the Romans disused it afterwards until the calendar was reformed by Julius Caesar. Thus there was no scientific astronomical knowledge worth mentioning among the primitive Greeks.

Immense research and learning have been expended by modern critics, to show the state of scientific astronomy among the Greeks. I am equally amazed at the amount of research, and its comparative worthlessness, for what addition to science can be made by an enumeration of the puerilities and errors of the Greeks, and how wasted and pedantic the learning which ransacks all antiquity to prove that the Greeks adopted this or that absurdity. [Transcriber's Note: Lengthy footnote relocated to chapter end.]

[Sidenote: Thales.]

[Sidenote: Anaximander and Anaximenes.]

But to return. The earliest historic name a.s.sociated with astronomy in Greece was Thales, the founder of the Ionic school of philosophers, born 639 B.C. He is reported to have predicted an eclipse of the sun, to have made a visit to Egypt, to have fixed the year at three hundred and sixty-five days, and to have determined the course of the sun from solstice to solstice. He attributed an eclipse of the moon to the interposition of the earth between the sun and moon; and an eclipse of the sun to the interposition of the moon between the sun and earth.

[Footnote: Sir G. G. Lewis, _Hist. of Astron._, p. 81.] He also determined the ratio of the sun's diameter to its apparent orbit. As he first solved the problem of inscribing a right-angled triangle in a circle, [Footnote: Diog. Laert, i. 24.] he is the founder of geometrical science in Greece. He left, however, nothing to writing, hence all accounts of him are confused. It is to be doubted whether in fact he made the discoveries attributed to him. His speculations, which science rejects, such as that water is the principle of all things, are irrelevant to a description of the progress of astronomy. That he was a great light, no one questions, considering the ignorance with which he was surrounded. Anaximander, who followed him in philosophy, held to puerile doctrines concerning the motions and nature of the stars, which it is useless to repeat. His addition to science, if he made any, was in treating the magnitudes and distances of the planets. He attempted to delineate the celestial sphere, and to measure time by a sun-dial.

Anaximenes of Miletus taught, like his predecessors, crude notions of the sun and stars, and speculated on the nature of the moon, but did nothing to advance his science on true grounds, except the construction of sun-dials. The same may be said of Herac.l.i.tus, Xenophanes, Parmenides, Anaxagoras. They were great men, but they gave to the world mere speculations, some of which are very puerile. They all held to the idea that the heavenly bodies revolved around the earth, and that the earth was a plain. But they explained eclipses, and supposed that the moon derived its light from the sun. Some of them knew the difference between the planets and the fixed stars. Anaxagoras scouted the notion that the sun was a G.o.d, and supposed it to be a ma.s.s of ignited stone, for which he was called an atheist.

[Sidenote: Socrates.]

[Sidenote: Pythagoras.]

Socrates, who belonged to another school, avoided all barren speculations concerning the universe, and confined himself to human actions and interests. He looked even upon geometry in a very practical way, so far as it could be made serviceable to land measuring. As for the stars and planets, he supposed it was impossible to arrive at a true knowledge of them, and regarded speculations upon them as useless. The Greek astronomers, however barren were their general theories, still laid the foundation of science. Pythagoras, born 580 B.C., taught the obliquity of the ecliptic, probably learned in Egypt, and the ident.i.ty of the morning and evening stars. It is supposed that he maintained that the sun was the centre of the universe, and that the earth revolved around it. But this he did not demonstrate, and his whole system was unscientific, a.s.suming certain arbitrary principles, from which he reasoned deductively. "He a.s.sumed that fire is more worthy than earth; that the more worthy place must be given to the more worthy; that the extremity is more worthy than the intermediate parts; and hence, as the centre is an extremity, the place of fire is at the centre of the universe, and that therefore the earth and other heavenly bodies move round the fiery centre." But this was no heliocentric system, since the sun moved like the earth, in a circle around the central fire. This was merely the work of the imagination, utterly unscientific, though bold and original. Nor did this hypothesis gain credit, since it was the fixed opinion of philosophers, that the earth was the centre of the universe, around which the sun and moon and planets revolved. But the Pythagoreans were the first to teach that the motions of the sun, moon, and planets, are circular and equable. Their idea that they emitted a sound, and were combined into a harmonious symphony, was exceedingly crude, however beautiful. "The music of the spheres" belongs to poetry, as well as the speculations of Plato.

[Sidenote: Eudoxus.]

Eudoxus, who was born 406 B.C., may be considered the founder of scientific astronomical knowledge among the Greeks. He is reputed to have visited Egypt with Plato, and to have resided thirteen years in Heliopolis, in constant study of the stars, communing with the Egyptian priests. His contribution to the science was a descriptive map of the heavens, which was used as a manual of sidereal astronomy to the sixth century of our era. He distributed the stars into constellations, with recognized names, and gave a sort of geographical description of their position and limits, although the constellations had been named before his time. He stated the periodic times of the five planets visible to the naked eye, but only approximated to the true periods.

The error of only one hundred and ninety days in the periodic time of Saturn, shows that there had been, for a long time, close observations.

Aristotle, whose comprehensive intellect, like that of Bacon, took in all forms of knowledge, condensed all that was known in his day in a treatise concerning the heavens. [Footnote: Delambre, _Hist. de l'Astron. Anc._, tom. i. p. 301.] He regarded astronomy as more intimately connected with mathematical science than any other branch of philosophy. But even he did not soar far beyond the philosophers of his day, since he held to the immobility of the earth--the grand error of the ancients. Some few speculators in science, like Herac.l.i.tus of Pontus and Hicetas, conceived a motion of the earth itself upon its axis, so as to account for the apparent motion of the sun, but they also thought it was in the centre of the universe.

[Sidenote: Meton.]

The introduction of the gnomon and dial into Greece advanced astronomical knowledge, since they were used to determine the equinoxes and solstices, as well as parts of the day. Meton set up a sun-dial at Athens in the year 433 B.C., but the length of the hour varied with the time of the year, since the Greeks divided the day into twelve equal parts. Dials were common at Rome in the time of Plautus, 224 B.C.; [Footnote: Ap. Gell., _N. A._, iii. 3.] but there was a difficulty of using them, since they failed at night and in cloudy weather, and could not be relied on. Hence the introduction of water-clocks instead.

[Sidenote: Aristarchus.]

Aristarchus is said to have combated (280 B.C.) the geocentric theory so generally received by philosophers, and to have promulgated the hypothesis "that the fixed stars and the sun are immovable; that the earth is carried round the sun in the circ.u.mference of a circle of which the sun is the centre; and that the sphere of the fixed stars having the same centre as the sun, is of such magnitude that the orbit of the earth is to the distance of the fixed stars, as the centre of the sphere of the fixed stars is to its surface." [Footnote: Lewis, p. 190.] This speculation, resting on the authority of Archimedes, was ridiculed by him; but if it were advanced, it shows a great advance in astronomical science, and considering the age, was one of the boldest speculations of antiquity. Aristarchus also, according to Plutarch, [Footnote: Plut., _Plac. Phil._, ii. 24.] explained the apparent annual motion of the sun in the ecliptic, by supposing the orbit of the earth to be inclined to its axis. There is no evidence that this great astronomer supported his heliocentric theory with any geometrical proof, although Plutarch maintains that he demonstrated it. [Footnote: _Quaest. Plat._, viii.

1.] This theory gave great offense, especially to the Stoics, and Cleanthes, the head of the school at that time, maintained that the author of such an impious doctrine should be punished. Aristarchus has left a treatise "On the Magnitudes and Distances of the Sun and Moon,"

and his methods to measure the apparent diameters of the sun and moon, are considered sound by modern astronomers, [Footnote: Lewis, p. 193.]

but inexact owing to defective instruments. He estimated the diameter of the sun at the seven hundred and twentieth part of the circ.u.mference of the circle, which it describes in its diurnal revolution, which is not far from the truth; but in this treatise he does not allude to his heliocentric theory.

[Sidenote: Archimedes.]

[Sidenote: Eratosthenes.]

Archimedes, born 287 B.C., is stated to have measured the distance of the sun, moon, and planets, and he constructed an orrery in which he exhibited their motions. But it was not in the Grecian colony of Syracuse, but of Alexandria, that the greatest light was shed on astronomical science. Here Aristarchus resided, and also Eratosthenes, who lived between the years 276 and 196 B.C. He was a native of Athens, but was invited by Ptolemy Euergetes to Alexandria, and placed at the head of the library. His great achievement was the determination of the circ.u.mference of the earth. This was done by measuring on the ground the distance between Syene, a city exactly under the tropic, and Alexandria situated on the same meridian. The distance was found to be five thousand stadia. The meridional distance of the sun from the zenith of Alexandria, he estimated to be 7 degrees 12', or a fiftieth part of the circ.u.mference of the meridian. Hence the circ.u.mference of the earth was fixed at two hundred and fifty thousand stadia, not far from the truth.

The circ.u.mference being known, the diameter of the earth was easily determined. The moderns have added nothing to this method. He also calculated the diameter of the sun to be twenty-seven times greater than of the earth, and the distance of the sun from the earth to be eight hundred and four million stadia, and that of the moon seven hundred and eighty thousand stadia--a very close approximation to the truth.

[Sidenote: Hipparchus.]

[Sidenote: Greatness of Hipparchus.]

Astronomical science received a great impulse from the school of Alexandria, and Eratosthenes had worthy successors in Aristarchus, Aristyllus, Apollonius. But the great light of this school was Hipparchus, whose lifetime extended from 190 to 120 years B.C. He laid the foundation of astronomy upon a scientific basis. "He determined,"

says Delambre, "the position of the stars by right ascensions and declinations; he was acquainted with the obliquity of the ecliptic. He determined the inequality of the sun, and the place of its apogee, as well as its mean motion; the mean motion of the moon, of its nodes and apogee; the equation of the moon's centre, and the inclination of its...o...b..t; he likewise detected a second inequality, of which he could not, for want of proper observations, discover the period and the law. His commentary on Aratus shows that he had expounded, and given a geometrical demonstration of, the methods necessary to find out the right and oblique ascensions of the points of the ecliptic and of the stars, the east point and the culminating point of the ecliptic, and the angle of the east, which is now called the nonagesimal degree. He could calculate eclipses of the moon, and use them for the correction of his lunar tables, and he had an approximate knowledge of parallax."

[Footnote: Delambre, _Hist. de l'Astron. Anc._, tom. i. p. 184.]

His determination of the motions of the sun and moon, and method of predicting eclipses, evince great mathematical genius. But he combined, with this determination, a theory of epicycles and eccentrics, which modern astronomy discards. It was, however, a great thing to conceive of the earth as a solid sphere, and reduce the phenomena of the heavenly bodies to uniform motions in of circular orbits. "That Hipparchus should have succeeded in the first great steps of the resolution of the heavenly bodies into circular motions is a circ.u.mstance," says Whewell, "which gives him one of the most distinguished places in the roll of great astronomers." [Footnote: _Hist. Ind. Science_, vol. i. p.

181.] But he even did more than this. He discovered that apparent motion of the fixed stars round the axis of the ecliptic, which is called the Precession of the Equinoxes, one of the greatest discoveries in astronomy. He maintained that the precession was not greater than fifty- nine seconds, and not less than thirty-six seconds. Hipparchus framed a catalogue of the stars, and determined their places with reference to the ecliptic, by their lat.i.tudes and longitudes. Altogether, he seems to have been one of the greatest geniuses of antiquity, and his works imply a prodigious amount of calculation.

[Sidenote: Posidonius.]

[Sidenote: The Roman Calendar.]

Astronomy made no progress for three hundred years, although it was expounded by improved methods. Posidonius constructed an orrery, which exhibited the diurnal motions of the sun, moon, and five planets.

Posidonius calculated the circ.u.mference of the earth to be two hundred and forty thousand stadia by a different method from Eratosthenes. The barrenness of discovery, from Hipparchus to Ptolemy, in spite of the patronage of the Ptolemies, was owing to the want of instruments for the accurate measure of time, like our clocks, to the imperfection of astronomical tables, and to the want of telescopes. Hence the great Greek astronomers were unable to realize their theories. Their theories were magnificent, and evinced great power of mathematical combination; but what could they do without that wondrous instrument by which the human eye indefinitely multiplies its power?--by which objects are distinctly seen, which, without it, would be invisible? Moreover, the ancients had no accurate almanacs, since the care of the calendar belonged to the priests rather than to the astronomers, who tampered with the computation of time for temporary and personal objects. The calendars of different communities differed. Hence Julius Caesar rendered a great service to science by the reform of the Roman calendar, which was exclusively under the control of the college of pontiffs. The Roman year consisted of three hundred and fifty-five days, and, in the time of Caesar, the calendar was in great confusion, being ninety days in advance, so that January was an autumn month. He inserted the regular intercalary month of twenty-three days, and two additional ones of sixty-seven days. These, together of ninety days, were added to three hundred and sixty-five days, making a year of transition of four hundred and forty-five days, by which January was brought back to the first month in the year after the winter solstice. And to prevent the repet.i.tion of the error, he directed that in future the year should consist of three hundred and sixty-five and one quarter days, which he effected by adding one day to the months of April, June, September, and November, and two days to the months of January, s.e.xtilis, and December, making an addition of ten days to the old year of three hundred and fifty-five. And he provided for a uniform intercalation of one day in every fourth year, which accounted for the remaining quarter of a day.

[Footnote: Suet., _Caesar_, 49; Plut., _Caesar_, 59.]

"Ille moras solis, quibus in sua signa rediret, Traditur exactis disposuisse notis.

Is decies senos tercentum et quinque diebus Junxit; et pleno tempora quarta die.

Hic anni modus est. In l.u.s.trum accedere debet Quae consummatur partibus, una dies."

[Footnote: Ovid, _Fast._, iii.]

[Sidenote: Caesar's labors.]

Caesar was a student of astronomy, and always found time for its contemplation. He is said even to have written a treatise on the motion of the stars. He was a.s.sisted in his reform of the calendar by Sosigines, an Alexandrian astronomer. He took it out of the hands of the priests, and made it a matter of pure civil regulation. The year was defined by the sun, and not, as before, by the moon.