i 4 SCIENCE IN GRECO-ROMAN ANTIQUITY 



according to the Babylonian custom, and that, on the 

 night of the observation, the degree occupied by the 

 sun at the instant of its setting be known. Then, if, 

 at the moment of which it is desired to ascertain the 

 time, the zodiacal stars on the eastern, western and 

 southern horizons be observed, the stars represented 

 on the sphere of the instrument can be brought into the 

 same position ; the degree in which the sun is situated 

 will then play exactly the same part as the shadow 

 of the end of the style during the day, and its position 

 with regard to the horary lines traced on the polos, 

 gives the required time." The Chaldeans thus suc- 

 ceeded in solving, by mechanical means, problems for 

 whose solution we have recourse to spherical 

 trigonometry. 



By dint of patient observations and in spite of the 

 imperfection of their instruments, they succeeded in 

 accumulating a considerable number of data, amongst 

 others ephemerides of the sun, moon, and principal 

 planets. The tablets of Cambyses, for example, give 

 a list of the conjunctions of the moon with five 

 planets, and also a list of the conjunctions of the 

 planets with each other. The celebrated astronomer 

 Kidinnu had calculated the synodic lunar month with 

 astonishing accuracy, to an error of 0-4 seconds 

 (29 days 12 hours 44 minutes 3-3 seconds instead of 

 2 -9 seconds). 1 



However, throughout all these splendid discoveries, 

 the distinctive features of Chaldean astronomy persist ; 

 being calculators and traders, the Chaldeans merely 

 sought to draw up numerical tables which would meet 

 their astronomical needs. They did not seek, as did the 

 Greeks, to represent geometrically the real or apparent 

 movements which explain the variable positions of the 

 heavenly bodies on the celestial sphere. 



1 2 Bigourdan, Astronomie, p. 217. 



