228 POPULAR LECTURES AND ADDRESSES. 



through large angles by attraction, that the in- 

 fluence of these purely attractive collisions is 

 preponderant over that of the comparatively very 

 rare impacts from actual contact. Thus, after all, 

 the train of speculation suggested by Davy's 

 Repulsive Motion does not allow us to escape 

 from the idea of true repulsion, does not do more 

 than let us say it is of no consequence, nor even 

 say this with truth, because, if there are impacts 

 at all, the nature of the force during the impact, 

 and the effects of the mutual impacts, however 

 rare, cannot be evaded in any attempt to realise 

 a conception of the kinetic theory of gases. And 

 in fact, unless we are satisfied to imagine the 

 atoms of a gas as mathematical points endowed 

 with inertia, and, as according to Boscovich, 

 endowed with forces of mutual positive and 

 negative attraction, varying according to some 

 definite function of the distance, we cannot avoid 

 the question of impacts, and of vibrations and 

 rotations of the molecules resulting from impacts, 

 and we must look distinctly on each molecule 

 as being either a little elastic solid, or a con- 



