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Updated: May 14, 2025
It considers the precession of the equinoxes, the discovery of Hipparchus, the full period for which is twenty-five thousand years. It gives a catalogue of 1,022 stars; treats of the nature of the Milky Way; and discusses, in the most masterly manner, the motions of the planets. This point constitutes Ptolemy's second claim to scientific fame.
During all this time Cleopatra and Ptolemy remained in the palace with Caesar, both ostensibly co-operating with him in his councils and measures for defending the city from Achillas. Cleopatra, of course, was sincere and in earnest in this co-operation; but Ptolemy's adhesion to the common cause was very little to be relied upon.
A regular messenger and carrier-dove service had been established between Alexandria and Pithom for the period of Ptolemy's relaxation; and the sovereign was accompanied not only by several of the chief councillors and secretaries, but artists and some of the Museum scientists with whom he was on specially intimate terms, who were to adorn the festival on the frontier with their presence, and cheer the invalid King, who needed entertainment.
It was Sir Henry M. Stanley who discovered the Ruwanzori mountain range, corresponding to the classical Mountains of the Moon, and who thus justified Ptolemy's view of the topography of Africa. For many years after Ptolemy, the work of exploring the sources of the Nile was entirely discontinued, and the solution of the problem was still wrapped in impenetrable mystery.
Ptolemy's efforts at exactness were baulked, as we have seen, by the supposed necessity of all the orbit planes passing through the earth, and if Copernicus had simply transferred this responsibility to the sun he would have done better.
Ptolemy's idea was that uniform motion in a circle must be provided, and since the motion was not uniform about the earth, A could not coincide with C; and since the motion still failed to be uniform about A or C, some point E must be found about which the motion should be uniform. This is not drawn to scale, but is intended to illustrate Kepler's modification of Ptolemy's excentric.
Before making a fresh start he looked for some simplification of the labour; and determined to adopt Ptolemy's assumption known as the principle of the bisection of the excentricity. A marked improvement in residuals was the result of this step, proving, so far, the correctness of Ptolemy's principle, but there still remained discordances amounting to eight minutes of arc.
But still more important discoveries were made in 1642 by an expedition sent out from Batavia under ABEL JANSSEN TASMAN to investigate the real extent of the southern land. After the voyages of the Leeuwin and De Nuyts it was seen that the southern coast of the new land trended to the east, instead of working round to the west, as would have been the case if Ptolemy's views had been correct.
These views of the ancients came once more to the attention of the learned, owing to the invention of printing and the revival of learning, when the Greek masterpieces began to be made accessible in Latin, chiefly by fugitive Greeks from Constantinople, which had been taken by the Turks in 1453. Ptolemy's geography was printed at Rome in 1462, and with maps in 1478.
The most noted of all the writings of Ptolemy is the work which became famous under the Arabic name of Almagest. From this it derived the word Almagest, by which Ptolemy's work continued to be known among the Arabs, and subsequently among Europeans when the book again became known in the West. Ptolemy's book, as has been said, is virtually an elaboration of the doctrines of Hipparchus.
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