Mr. Exley on Mossotti's Theory of Physics, 497 



completely conclusive, till established at least in some re- 

 markable particular cases, as is allowed on all hands, on ac- 

 count of the hypotheses, substitutions, and omissions of small 

 quantities in the progress of the reasonings. 



The theory is this : M. Mossotti supposes " matter to con- 

 sist of two sorts, each of which repels its own particles, direct- 

 ly as the mass, and inversely as the squares of their distances, 

 while each attracts those of the other kind according to the 

 same law." Babbage, p. 164. 



Mossotti supposes the forces to be directed towards central 

 solids, which he assumes to be small and spherical ; he also 

 considers one of the two sorts to be diffused through universal 

 space, and this sort he calls aether, its elements Mr. Babbage 

 calls atmospheric particles ; and the other sort, of which com- 

 mon bodies are formed, Mossotti calls molecules. 



The two following principles comprehend my theory ; viz. 

 1st. Every atom of matter consists of an indefinite sphere of 

 force, which varies inversely as the square of the distance from 

 the centre ; and this force acts towards the centre, and is call- 

 ed attraction, at all distances, except in a small concentric 

 sphere, in which it acts from the centre, and is there called 

 repulsion. 2nd. The differences and distinctions of atoms 

 arise from differences in their absolute forces, and in the 

 radii of their spheres of repulsion. 



According to this theory central solids are unnecessary. It 

 was observed by the venerable Dr. Dalton (August 23rd, 

 1836) in a discussion of the subject at the meeting of the 

 British Association in Bristol, that he could not give up the 

 idea of solid atoms : my reply was, the theory does not require 

 it, provided we may have the solids as small as we please ; 

 in that case they can do neither good nor harm. A very 

 learned and universally admired professor of Cambridge, who 

 honoured my paper with some judicious remarks, previously to 

 its being read on that occasion, objected that " it would be 

 impossible to identify such a repulsive force with the attractive 

 force, because the law of continuity would be violated." Now 

 I humbly conceive we do not in general determine the identity 

 of a force by its direction, but rather by the law of its action, 

 which in these principles is continuous. Why may not this 

 change be at once ? It must appear that all who admit alterna- 

 tions of attraction and repulsion, must admit such violation, if 

 it be one, of continuity ; for the change of direction is equally 

 so, whether it be from a finite to a finite, or from an infinitely 

 small attraction to an infinitely small repulsion. 



It is manifest that this theory provides for an infinity of 

 sorts of matter, and that the centres of atoms can in no case 

 coincide. Various sorts of atoms according to the above prin- 



ThirdScrics. Vol. 11. No. 70. Dec. 1837. 3.S 



