258 THE FOEEST LANDS OF FINLAND. 



and what happens thus to the heavier masses happens 

 there or further in advance, in succession as the velocity is 

 reduced, to others of lesser weight. 



But he also refers, as have other writers on Alpine tor- 

 rents, to the more remarkable phenomenon of large stones 

 seen bounding before the advancing wave of a mountain 

 torrent. In regard to this he writes : ' Some of the 

 effects of torrents have appeared so extraordinary that, the 

 the law of torrentiality not having been ascertained, the 

 imagination set to work to seek out fanciful explanations 

 of what was seen. 



' Thus, for example, has it been with the general 

 allegation, that at the moment of flood large stones set 

 off of themselves, rolling in advance before the current had 

 touched them, under impulse from a current of air preced- 

 ing the advancing head of waters. 



' Eye-witnesses, and these grave men, have affirmed 

 this fact to myself; and M. Surell has collected numerous 

 testimonies of this phenomenon, and has sought to 

 account for it theoretically. In reality, the fact as 

 reported is absolutely impossible. Resistance increases as 

 the square of the velocity. Let a calculation be made, 

 from the velocity necessary to a current of air to displace 

 a stone no larger than an egg ; what velocity would require 

 to be imparted to a current of air capable of displacing a 

 stone such as some of those of which this has been told, 

 which must have been at least 50 centimetres, or 20 inches 

 in diameter ! The thing alleged is physically impossible ; 

 and it must be remarked that the people who allege they 

 have seen those things occur under their eyes, at a few 

 paces from them, do not dream that if they had been 

 caught in such a current of air they would, at least, have 

 felt it ! 



'When these witnesses are cross-questioned, they all 

 declare that they have seen the stones rolling dry before 

 them ; but no one says he has seen these stones begin to 

 move. The witnesses are trustworthy, in so far as it is 

 true that the stones were seen rolling before their eyes ; 



