368 SCIENCE PROGRESS. 



is announced if we were able to ascertain by a complete enu- 

 meration of the different physical agents that none of them 

 is capable of producing it the impossibility of the phenom- 

 enon would be the inevitable result and consequently the 

 falsity of the account. But on the other hand, when we 

 find a cause which establishes the possibility of it, if sound 

 logic forbids us to ascribe it exclusively to this cause, it 

 commands us at the same time to substitute doubt for com- 

 plete negation and to employ every means possible of con- 

 firming the fact, because it is not repugnant to the general 

 laws of Nature." 



This very guarded and somewhat curious statement is 

 explained by the fact that Laplace and Poisson had calcu- 

 lated that a body projected from the moon would require 

 only a velocity five times as great as that of a bullet of a 

 twenty-four pounder, discharged with a quantity of gun- 

 powder equal to half its own weight, to reach the earth after 

 a journey of sixty-four hours, and would arrive with a velocity 

 of 31,000 feet a second. It is evident that the accounts of . 

 the falls themselves were by this time no longer discredited, 

 and that even the lightning theory was losing its adherents. 



In 1803 Olbers, who had at first asserted that the Sienna 

 stones were from Vesuvius, is led by the similarity of the sky- 

 stones in different parts of the world to agree that they had 

 a common origin and probably came from the moon. The 

 chemist Vauquelin also inclined to the moon theory ; it is 

 evident that the absence of atmosphere there would account 

 for the stones leaving a lunar volcano without retardation and 

 and also without experiencing oxidation. Writing of the Bar- 

 botan fall which took place in 1789 he says : " Some peasants 

 brought stones which they said were the result of the fall of 

 the meteor ; but at that period they were laughed at. What 

 they said was considered as fables — and those to whom the 

 stones were offered would not accept of them. The peasants 

 would now have more reason to laugh at the philosophers." 



Even at this period, however, when it began to be sus- 

 pected that stones really fell from the sky and that they 

 may have a common origin, it was by no means universally 

 conceded that they were extraterrestrial. 



