VI.] ON THE METHOD OF ZADIG. 137 



But astronomy is not less remarkable for its power 

 of retrospective prophecy. 



Thales, oldest of Greek philosophers, the dates of 

 whose birth and death are uncertain, but who flourished 

 about 600 B.C., is said to have foretold an eclipse of the 

 sun which took place in his time during a battle 

 between the Medes and the Lydians. Sir George Airy 

 has written a very learned and interesting memoir 1 in 

 which he proves that such an eclipse was visible in 

 Lydia on the afternoon of the 28th of May in the 

 year 585 B.C. 



No one doubts that, on the day and at the hour 

 mentioned by the Astronomer Koyal, the people of 

 Asia Minor saw the face of the sun totally obscured. 

 But, though we implicitly believe this retrospective 

 prophecy, it is incapable of verification. In the 

 total absence of historical records, it is impossible 

 even to conceive any means of ascertaining directly 

 whether the eclipse of Thales happened or not. All 

 that can be said is, that the prospective prophecies 

 of the astronomer are always verified ; and that, 

 inasmuch as his retrospective prophecies are the re- 

 sult of following backwards, the very same method as 

 that which invariably leads to verified results, when 

 it is worked forwards, there is as much reason for 

 placing full confidence in the one as in the other. 

 .Retrospective prophecy is therefore a legitimate func- 

 tion of astronomical science ; and if it is legitimate for 

 one science it is legitimate for all ; the fundamental 



1 " On the Eclipses of Agathocles, Thales, and Xerxes," Philosophical 

 Transactions, vol. cxliii. 



