26 PROFESSOR KELLAND, ON MOLECULAR EQUILIBRIUM. 



The phenomena of electricity and magnetism did indeed suggest 

 hypotheses respecting the internal constitution of bodies, but these 

 hypotheses, for the most part, were only partial ones. Those of 

 iEpinus, Cavendish, and Franklin, fully establish a disposition of dif- 

 ferent sets of particles, but leave the possibility of such a disposition 

 as consistent with the conditions of equilibrium to other hypotheses of 

 a nature totally different from the one applied. With one or two ex- 

 ceptions it would appear, that all writers have regarded the molecular 

 force as of a nature either distinct from that of the attractions and 

 repulsions of the electric particles, or as the fundamental expression 

 of which the law, in the latter case, is only a limiting form. 



About the middle of the last century, however, Dr Knight published 

 his " Attempt to explain all the Phenomena of Nature by means of 

 two Principles, Attraction and Repulsion." The hypothesis adopted in 

 this work, appears to be nearly the same as that usually adopted by 

 theorists in Chemistry of the present day, and which is not essentially 

 different from that which forms the basis of the present Memoir, with 

 the exception, that the Author supposes the law of force to be the 

 inverse power of the distance. Bodies are imagined to be formed 

 of combinations of two groups of particles acting differently on each 

 other, the one set mutually attractive, the other mutually repulsive; 

 the former, by peculiar arrangements aggregated together, determine 

 the nature of different substances ; whilst the latter are collected around 

 these groups, and form their atmospheres. I regret that I have not 

 been able to meet with Dr Knight's work, which appears from the 

 notices of it, to have been a sound and admirable treatise. 



A few years later appeared Boscovich's " Theoria Philosophic Natu- 

 ralis ad unicam legem virium, in Naturd existentium redacta" a work 

 which from its title professes the reduction of all forces to one and 

 the same law. As that law will be found to be the conclusion from 

 another more simple law, I shall briefly state its principal features. 



(l). "The atoms of matter are endued with attractive or repulsive 

 forces to one another, of which the law of variation is the same for 

 all." 



