592 ' LECTUnE XLVIII. 



occurred to men of so great talents, that the only way to become accurately ac- 

 quainted with nature, is to institute experimental inquiries throughout her works. 



Thales of Miletus, who was born in the year 640 before Christ, having 

 travelled and studied in Egypt, founded, on his return, the Ionian school of 

 philosophy, in which he taught the sphericity of the earth, and the obliquity 

 of the ecliptic with respect to the equator. He also explained the true causes 

 of eclipses, which he was even able to foretel, unquestionably by means of 

 the information that he had obtained from the Egyptian priests. 



Pythagoras of Samos was born 590 years before Christ; he probably profited 

 by the information which Thales had acquired, and travelled also into Egypt 

 for his further improvement. It is conjectured that he was acquainted with 

 the diurnal and annual motions of the earth, but he did not publicly profess 

 the true system of the world. It was taught after his death, by his disciple 

 Philolaus, about the year 450, as well as by Nicetas, and by others of the 

 school. They considered all the planets as revolving round the sun, and as 

 inhabited globes; and they understood that the comets were only eccentric 

 planets. Some time after this, the lunar period of Meto was publicly made 

 known at the Olympic games, and was universally adopted as the basis of 

 the calendar. (Plate XXXVIII. Fig. 527.) 



The next occurrence which deserves to be noticed, with respect to astronomy 

 is the foundation of the school of Alexandria, which was the first source of 

 accurate and continued observations. Upon the death of Alexander, and the 

 subsequent division of his empire, the province of Egypt fell to the lot of 

 Ptolemy Soter; a prince whose love of science, and whose munificence towards 

 its professors, attracted to his capital a great number of learned men from 

 various parts of Greece. His son, Ptolemy Philadelphus, continued and in- 

 creased the benefits conferred on them by his father, and built the magnificent 

 edifice which contained, together with the celebrated library, collected by 

 Demetrius] Phalereus, an observatory, furnished with the necessary books 

 and instruments. The first astronomers, who were appointed to occupy this 

 building, Avere Aristyllus and Timocharis; they flourished about 300 years 

 before Christ, and observed with accuracy the places of the principal stars of 



