44, 45] Hipparchus 6 1 



If then the path of the moon, as seen from the centre 

 of the earth, were known, then the path of the moon as 

 seen from any particular station on the earth could be 

 deduced by allowing for parallax, and the conditions of 

 an eclipse of the sun visible there could be computed 

 accordingly. 



From the time of Hipparchus onwards lunar eclipses 

 could easily be predicted to within an hour or two by 

 any ordinary astronomer ; solar eclipses probably with less 

 accuracy ; and in both cases the prediction of the extent of 

 the eclipse, i.e. of what portion of the sun or moon would 

 be obscured, probably left very much to be desired. 



44. The great services rendered to astronomy by Hippar- 

 chus can hardly be better expressed than in the words of 

 the great French historian of astronomy, Delambre, who is 

 in general no lenient critic of the work of his predecessors : 



11 When we consider all that Hipparchus invented or perfected, 

 and reflect upon the number of his works and the mass of 

 calculations which they imply, we must regard him as one of 

 the most astonishing men of antiquity, and as the greatest of all 

 in the sciences which are not purely speculative, and which 

 require a combination of geometrical knowledge with a 

 knowledge of -phenomena, to be observed only by diligent 

 attention and refined instruments."* 



45. For nearly three centuries after the death of Hippar- 

 chus, the history of astronomy is almost a blank. Several 

 textbooks written during this period are extant, shewing 

 the gradual popularisation of his great discoveries. Among 

 the few things of interest in these books may be noticed 

 a statement that the stars are not necessarily on the sur- 

 face of a sphere, but may be at different distances from 

 us, which, however, there are no means of estimating ; a 

 conjecture that the sun and stars are so far off that the earth 

 would be a mere point seen from the sun and invisible 

 from the stars ; and a re-statement of an old opinion 

 traditionally attributed to the Egyptians (whether of the 

 Alexandrine period or earlier is uncertain), that Venus and 

 Mercury revolve round the sun. It seems also that in this 

 period some attempts were made to explain the planetary 



* Histoire de I 'Astronomic Anctenne, Vol. I., p. 185. 



