CHAPTER IX. SCIENTIFIC KNOWLEDGE AMONG THE ROMANS.
[Footnote: Ovid, Fast., iii.]
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 assisted 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.
Thus the Romans were the first to bring the scientific knowledge of the Greeks into practical use; but while they measured the year with a great approximation to accuracy, they still used sun-dials and water-clocks to measure diurnal time. And even these were not constructed as they should have been. The hours on the sun-dial were all made equal, instead of varying with the length of the day, so that the hour varied with the length of the day. The illuminated interval was divided into twelve equal parts, so that, if the sun rose at five A.M. and set at eight P.M., each hour was equal to eighty minutes. And this rude method of measurement of diurnal time remained in use till the sixth century. But clocks, with wheels and weights, were not invented till the twelfth century.
The earlier Greek astronomers did not attempt to fix the order of the planets; but when geometry was applied to celestial movements, the difference between the three superior planets and the two inferior was perceived, and the sun was placed in the midst between them, so that the seven movable heavenly bodies were made to succeed one another in the following order: 1. Saturn; 2. Jupiter; 3. Mars; 4. The Sun; 5. Venus; 6. Mercury; 7. The Moon. Archimedes adopted this order, which was followed by the leading philosophers. [Footnote: Lewis, p. 247.]
[Ptolemy and his system.]
The last great light among the ancients in astronomical science was Ptolemy, who lived from 100 to 170 A.D. in Alexandria. He was acquainted with the writings of all the previous astronomers, but accepted Hipparchus as his guide. He held that the heaven is spherical and revolves upon its axis; that the earth is a sphere, and is situated within the celestial sphere, and nearly at its centre; that it is a mere point in reference to the distance and magnitude of the fixed stars, and that it has no motion. He adopted the views of the ancient astronomers, who placed Saturn, Jupiter, and Mars next under the sphere of the fixed stars, then the sun above Venus and Mercury, and lastly the moon next to the earth. But he differed from Aristotle, who conceived that the earth revolves in an orbit round the centre of the planetary system, and turns upon its axis - two ideas in common with the doctrines which Copernicus afterward unfolded. But even he did not conceive the heliocentric theory that the sun is the centre of the universe. Archimedes and Hipparchus both rejected this theory.
In regard to the practical value of the speculations of the ancient astronomers, it may be said that, had they possessed clocks and telescopes, their scientific methods would have sufficed for all practical purposes. The greatness of modern discoveries lies in the great stretch of the reasoning powers, and the magnificent field they afford for sublime contemplation. "But," as Sir G. Cornwall Lewis remarks, "modern astronomy is a science of pure curiosity, and is directed exclusively to the extension of knowledge in a field which human interests can never enter. The periodic time of Uranus, the nature of Saturn's ring, and the occupation of Jupiter's satellites, are as far removed from the concerns of mankind as the heliacal rising of Sirius, or the northern position of the Great Bear." This may seem to be a utilitarian view with which those philosophers, who have cultivated science for its own sake, finding in the same a sufficient reward, as in truth and virtue, can have no sympathy.
[Result of ancient investigations.]
The upshot of the scientific attainments of the ancients, in the magnificent realm of the heavenly bodies, would seem to be that they laid the foundation of all the definite knowledge which is useful to mankind; while in the field of abstract calculation they evinced reasoning and mathematical powers which have never been surpassed. Eratosthenes, Archimedes, and Hipparchus were geniuses worthy to be placed by the side of Kepler, Newton, and La Place. And all ages will reverence their efforts and their memory. It is truly surprising that, with their imperfect instruments, and the absence of definite data, they reached a height so sublime and grand. They explained the doctrine of the sphere and the apparent motions of the planets, but they had no instruments capable of measuring angular distances. The ingenious epicycles of Ptolemy prepared the way for the elliptic orbits and laws of Kepler, which, in turn, conducted Newton to the discovery of the laws of gravitation - the grandest scientific discovery in the annals of our race.
[Ancient Greek geometers.]