28 PROFESSOR KELLAND, ON MOLECULAR EQUILIBRIUM. 



in the Memoir where he detects the insufficiency of Laplace's hypo- 

 thesis of capillary attraction, attempt to ascend higher in the investiga- 

 tion. In his Theory of Heat too, he introduces discrete molecules only 

 for the purpose of generalizing the problems of conduction and ra- 

 diation, without attempting to solve those of expansion and crystal- 

 lization : so that he makes no progress whatever in the explanation of 

 phenomena. 



3. In my Memoir on Dispersion, I endeavoured to shew that the law 

 of the inverse square of the distance, is that of the attraction or repulsion 

 of the particles of light, and in subsequent Memoirs, I have endeavoured 

 to reduce some of the phenomena of sound and heat to the same 

 law. Nothing, however, was effected with respect to the equilibrium 

 of the molecules. The latter object has lately been accomplished, at 

 least partially, by M. Mossotti, in a Memoir "On the Forces which 

 regulate the Internal Constitution of Bodies." The hypothesis of Mossotti 

 is the same as Dr Knight's, except that the forces vary inversely as 

 the square of the distance. It is proved, that one set of particles may 

 have an atmosphere of another set, the density of which varies rapidly 

 in receding from the surface of the former. M. Mossotti then endeavours 

 to find the conditions of equilibrium of a particle of the first or the 

 material set. It is ion this point that I conceive M. Mossotti's hypothesis 

 completely fails. The law of action of two particles as deduced by 

 M. Mossotti, is composed of two parts, a repulsive part which vanishes 

 when the distance is sensible, and an attractive part which varies in- 

 versely as the square of the distance. Now when it is borne in mind 

 that the whole set of forces acting on any particle must be sufficient 

 to retain that particle in equilibrium at a certain distance from the one 

 next to it, we shall perceive that this law of action requires that the 

 mutual distance, or the density of the particles, should vary as the 

 magnitude of the body. I do not mean to assert, that the density 

 should be increased in the same ratio as the mass is increased, but that 

 it must be so increased, that the repulsive force of the adjacent particles 

 should be very nearly in the proportion of the linear magnitude of the 

 body. I cannot think this a probable, hardly a possible, condition of 

 matter. The state of the surface may depend, and probably does so. 



