10 ON THE METHOD OF ZADIG I 



for our well grounded confidence that monuments 

 and works of art or artifice, have never been pro- 

 duced by causes different in kind from those to 

 which they now owe their origin. And geology, 

 which traces back the course of history beyond 

 the limits of archaeology, could tell us nothing 

 except for the assumption that, millions of years 

 ago, water, heat, gravitation, friction, animal and 

 vegetable life, caused effects of the same kind as 

 they now cause. Nay, even physical astronomy, 

 is so far as it takes us back to the uttermost 

 point of time which palsetiological science can 

 reach, is founded upon the same assumption. If 

 the law of gravitation ever failed to be true, even 

 to a small extent, for that period, the calculations 

 of the astronomer have no application. 



The power of prediction, of prospective pro- 

 phecy, is that which is commonly regarded as 

 the great prerogative of physical science. And 

 truly it is a wonderful fact that one can go into 

 a shop and buy for a small price a book, the 

 " Nautical Almanac," which will foretell the 

 exact position to be occupied by one of Jupiter's 

 moons six months hence ; nay, more, that, if it 

 were worth 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 



