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Updated: May 1, 2025
No one pretends that Ptolemy is to be compared with the Rhodesian observer as an original investigator, but as a popular expounder his superiority is evidenced in the fact that the writings of Ptolemy became practically the sole astronomical text-book of the Middle Ages both in the East and in the West, while the writings of Hipparchus were allowed to perish.
Two centuries before the time of Hipparchus he conceived a doctrine of spheres which Aristotle found most interesting, and which served to explain, along the lines we have just followed, the observed motions of the heavenly bodies. Calippus, the reformer of the calendar, is said to have carried an account of this theory to Aristotle.
But it is not merely the sun which was observed to vary in the speed of its orbital progress; the moon and the planets also show curious accelerations and retardations of motion. The moon in particular received most careful attention from Hipparchus.
The mechanism of the heavens, from his point of view, has however, been greatly misunderstood. Neither he nor Hipparchus ever intended that theory as anything more than a geometrical fiction. It is not to be regarded as a representation of the actual celestial motions.
In the shade of the Museion a brilliant assembly Ptolemy, Euclid, Hipparchus, Apollonius, and Eratosthenes made great discoveries and added materially to the sum of human knowledge. Here Euclid wrote his immortal "Elements;" and Herophilos, the father of surgery, added valuable information to the knowledge of anatomy.
Hipparchus said of him, perhaps half jestingly, that he had studied astronomy as a geographer and geography as an astronomer. It is not quite clear whether the epigram was meant as compliment or as criticism. Similar phrases have been turned against men of versatile talent in every age.
Hipparchus also framed a catalogue of the stars, and determined their places with reference to the ecliptic by their latitudes and longitudes. Altogether he seems to have been one of the greatest geniuses of antiquity, and his works imply a prodigious amount of calculation. Astronomy made no progress for three hundred years, although it was expounded by improved methods.
Proclus's treatises on Plato's Republic are complete only in the Vatican manuscripts. Of these Mai only published fragments, but an English theologian, Alexander Morus, took notes from the manuscript when it was in Florence, and quoted from it in a commentary on the Epistle to the Hebrews. Proclus says that his information is derived from letters, "some written by Hipparchus, others by Arrhidæus."
"That Hipparchus should have succeeded in the first great steps of the resolution of the heavenly bodies into circular motions is a circumstance," says Whewell, "which gives him one of the most distinguished places in the roll of great astronomers."
Meanwhile the Moors were leaders of science in the west, and Arzachel of Toledo improved the solar tables very much. Ulugh Begh, grandson of the great Tamerlane the Tartar, built a fine observatory at Samarcand in the fifteenth century, and made a great catalogue of stars, the first since the time of Hipparchus. Nicolai Copernicus, a Sclav, was born in 1473 at Thorn, in Polish Prussia.
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