PROFESSOR KELLAND, ON MOLECULAR EQUILIBRIUM. 27 



(2). "Action and reaction are equal." 



(3). "The nature of the force is such that at different distances 

 it is attractive and repulsive alternately, so that a particle in reced- 

 ing from another, is first repelled, then attracted, then again repelled, 

 and so on." 



(4). " When the distance is indefinitely diminished, the force is re- 

 pulsive and is indefinitely increased; and when the distance is inde- 

 finitely increased, the force is attractive and diminishes as the inverse 

 square of the distance." 



Such are the general features of Boscovich's law of molecular action. 

 It will be our endeavour to deduce from an hypothesis not very dif- 

 ferent from that of Knight, a law resembling the above in its general 

 features. 



2. Notwithstanding the long interval that has elapsed since the 

 publication of Boscovich's work, very little has been done on the sub- 

 ject, except by way of application, until very lately. Capillary attrac- 

 tion is a phenomenon, the solution of which, clearly requires a molecular 

 hypothesis ; but, unfortunately, the nature of the question is such that 

 it is satisfied without the aid of any specific restriction to the law, 

 except that it should be one which very rapidly diminishes as the dis- 

 tance increases, and is insensible at distances appreciable by our senses. 

 Hence, we know that Laplace in his Mecanique Celeste, and Poisson 

 after him, have not cared to assume any particular law of force, and 

 even if they had, no means would have been found for its verification. 

 One result of this fact appears to be, that the circumstance of an 

 active force of this nature being sufficient to explain a phenomenon 

 totally different in character from those of cohesion and combination, by 

 which it is obviously suggested, induced Laplace himself to the belief 

 that this was the ultimate law. If such be not the case, I am unable 

 to account for his adoption of such a law, absurd as it appears, in 

 his explanation of the phenomena of heat. It would have been sup- 

 posed, that this was an opportunity of applying the beautiful analysis 

 of the former parts of his work to the reduction of the molecular law 

 to some simple form. But such is not the case, nor does Poisson, even 



D 2 



