By Professor Pell. 3 



gases in so many of their properties, that it is impossible not to 

 believe that they are governed by the same laws. If the molecules 

 of hydrogen repel one another at certain distances, we cannot 

 doubt that the same is true with respect to chlorine, and carbonic 

 acid gas, and steam. Indeed it would be diflB.cult to know 

 where to draw the line between hydrogen and the most refractory 

 solid. But if the molecules of carbonic acid gas be brought near 

 enough together, they undoubtedly attract, and at still shorter 

 distances again repel one another. If we assume the existence 

 of isolated atoms, there seems no escape from the doctrine of an 

 alternation of actual attractions and repulsions. 



Sir Humphry Davy supposed that the repulsive forces 

 between the particles of matter might be of a nature analogous 

 to thar which keeps the planets from falling into the sun, or to 

 what commonly goes by the name of centrifugal force. Except 

 that this view of the case is mentioned with approval by a recent 

 writer, I should not have thought it necessary to make use of any 

 arguments to shew that the complicated actions which take place 

 between particles of matter caunot be accounted for by Newton's 

 Law of Attraction alone. That the particles of a solid body should 

 be not only kept apart, but in permanent general relative 

 positions, by centrifugal force alone, seems to me utterly incon- 

 ceivable, under any known mechanical laws. It may be demon- 

 strated moreover, assuming the theory of atoms, that the cohesive 

 forces of any substance, having any appreciable tenacity, are not 

 only greater, but many millions of times greater, than what 

 would be caused by Newton's Law. It is so far certain then, 

 that that law is not absolutely universal, but is replaced or 

 supplemented by something totally different at very short 

 distances. 



The atoms or particles of a solid body certainly seem to be in a 

 position of stable equilibrium, or rather to be vibrating about such 

 a position ; and there seems no good reason for doubting that such 

 is, not apparently only, but really the case. The following con- 

 siderations seem to me to show conclusively, that it cannot be 

 the law of nature that two atoms should attract one another, 

 for all distances however small. It seems natural to suppose 

 that the total quantity of heat, or energy in any solid body, or 

 collection of atoms, is finite, and capable of being expressed as 

 some function of the masses, velocities, mutual actions and 

 relative co-ordinates of the atoms. Now if the atoms attract 

 one another for all distances however small, up to actual contact, 

 then the potential energy, or that due to any relative position of 

 the atoms, would depend partly upon the magnitude and internal 

 constitution of the atoms themselves, and would be, humanly 

 speaking, incapable of definite expression. If the atoms be sup- 



