310 



GREEK SCIENCE. 



Autolycus. 

 B. C.' 300. 



Cycle of 

 nineteen 

 years 

 invented. 

 B.C. 433. 



the appearances presented by the revolution of a sphered Thales, or 

 his immediate successors, had maintained the spherical form of the 

 earth, and imagined and named the most important circles in the 

 sphere of the heavens. After this, the application of geometry to 

 determine the risings, settings, and motions of the stars was an obvious 

 step, and seems to have been early made. It does not appear to have 

 led to any very recondite consequences ; and may be adequately judged 

 of from the ancient and curious treatise on the sphere still extant, and 

 written by AUTOLYCOS, who lived about the time of Alexander. For 

 an account of this work, and of other early Greek astronomers, see 

 the. * History of Astronomy.' * Of Eudoxus, one of the most emi- 

 nent of them, we may further notice Delambre's opinion, that he pos- 

 sessed an artificial globe, such as we may conceive the skill of that 

 time able to produce ; and that having marked upon it the places of 

 the stars, with no great exactness, he determined their risings and 

 settings by means similar to what is now understood by " the use 

 of the globes." The results of this method he published in a work 

 which we may consider of great importance, as having given rise not 

 only to the poetical paraphrase of Arctus, but to the valuable com- 

 mentary of Hipparchus. 



The other astronomical opinions of the Greek philosophers were less 

 precise and correct. The true system of the universe had indeed been 

 maintained by Pythagoras, but the minds, even of philosophers, were 

 not yet ripe for it ; and except that it was occasionally revived, as for 

 instance by Aristarchus of Samos, a little before Archimedes, it slept 

 till the time of Copernicus. Aristotle pretended to confute it ; and 

 Plato's opinions, though often borrowed from the Pythagoreans, have 

 no tinge of that part of their philosophy. Yet he is said to have 

 adopted in his old age the system which places the sun in the centre 

 of the universe. He had also the merit of having recommended 

 mathematics to the more particular attention of astronomers ; but ap- 

 parently this was done with the hope of discovering imaginary relations 

 among the parts of the universe : such, perhaps, as afterwards haunted 

 the mind of Kepler; and though unfounded in themselves, led him, 

 by singular good fortune, to the true laws of the solar system. Eu- 

 doxus, already mentioned as the disciple of Plato, appears to be the 

 author of that cumbrous hypothesis of crystalline spheres, which gene- 

 rally, but erroneously, has the name of Ptolemy attached to it. It is 

 not to be found in the works of that great astronomer, though it was 

 adopted by Aristotle and others of the ancients. 



The most important practical result of the astronomy of those times 

 was the invention of the cycle of nineteen years (tj/vea^Kcttr/jptc), for 

 the purpose of making the solar and lunar year coincide. It is said 

 (Geminus, c. 6) to have been produced for the approbation of the 

 Athenians, by METON and EUCTEMON, and adopted B. c. 433 ; and it 

 so far answers its purpose, that it is still in use, under the name of 

 1 Page 334 of this volume. 



