144 OX THE METHOD OF ZADIG. 



while, the Astronomer Royal could furnish us with as 

 infallible a prediction applicable to 1980 or 2980. 



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 writ- 

 ten a very learned and interesting memoir* 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 Royal, 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 astron- 

 omer are always verified ; and that, inasmuch as his 

 retrospective prophecies are the result of following back- 

 wards, 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 



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

 Transactions, vol. cxliii. 



