16 THE HISTORY OF SCIENCE 



self capable of applying them to the solution of par- 

 ticular problems. In the presence of the Egyptian 

 priests, to which class he was solely indebted for in- 

 struction, Thales demonstrated a method of measur- 

 ing the height of a pyramid by reference to its 

 shadow. And again, on the basis of his knowledge 

 of the relation of the sides of a triangle to its angles, 

 he developed a practical rule for ascertaining the 

 distance of a ship from the shore. 



The philosophical mind of Thales laid hold, no 

 doubt, of some of the essentials of astronomical sci- 

 ence. The particulars usually brought forward to 

 prove his originality tend rather to show his indebt- 

 edness to the Babylonians. The number of days in 

 the year, the length of the synodic month, the rela- 

 tion of the sun's apparent diameter to the ecliptic, 

 the times of recurrence of eclipses, were matters that 

 had long been known to the Babylonians, as well as 

 to the Chinese. However, he aroused great interest 

 in astronomy among the Greeks by the prediction 

 of a solar eclipse. This was probably the eclipse of 

 585 B.C., which interrupted a fierce battle between 

 the Medes and the Lydians. The advice of Thales 

 to mariners to steer by the Lesser Bear, as nearer 

 the pole, rather than by the Great Bear, shows also 

 that in his astronomical studies as in his geometri- 

 cal he was not indifferent to the applications of 

 scientific knowledge. 



In fact, some writers maintain that Thales was 

 not a philosopher at all, but rather an astronomer 

 and engineer. We know very little of his purely 

 speculative thought. We do know, however, that he 

 arrived at a generalization fantastic to most minds 



