296 cosmic ruiLusorn r. [ PT . n. 



"be the resultant between the lines of greatest traction and of 

 least resistance. 



In conclusion let us observe that in many cases the total 

 amount of traction is so small compared to the total amount 

 of resistance, that for practical purposes it may be neglected ; 

 and vice versd. Thus, when a meteor falls upon the earth, 

 we may neglect the resistance of the atmosphere, and say 

 that the meteor follows the line of greatest traction ; and 

 when a volcano throws up a column of lava, we may neglect 

 the effects of gravity, and say that for the time being the lava 

 follows the line of least resistance. We shall thus, without 

 any considerable inaccuracy, avoid cumbrous verbiage; and 

 in the case of molecular motions propagated through masses 

 of matter, with which our exposition is chiefly concerned, it 

 is sufficiently accurate to say that motion follows the line of 

 least resistance. 



