498 Mr. Exley's Remarks on M. Mossotti's Theory qf Physics, 



ciples may be assumed, and calculations made to deduce the 

 phenomena a priori; but in order that such phenomena may 

 agree with those actually observed, we must be guided in such 

 assumptions by the indications of nature: on this ground I 

 have admitted three classes: 1st. Tenacious atoms, distin- 

 guished into sorts by moderate differences in their absolute 

 forces and spheres of repulsion. 2nd. Electrical atoms, being 

 such as have a much less absolute force, say a thousand times 

 less than the least powerful of the first class. 3rd. iEthereal 

 atoms, whose absolute forces may be several million times less 

 than those of the 2nd class, and like the first consisting of 

 several sorts. If we suppose a due quantity of each variety 

 present, it is manifest that the atoms of the first class will at- 

 tract to their spheres of repulsion dense atmospheres of electric 

 and aethereal atoms, whose centres will be found within the 

 spheres of repulsion of contiguous atoms : and such a body as 

 the earth will retain an atmosphere of such matter if present ex- 

 tending several hundred miles, giving rise to such repulsions 

 as are observed. 



Mr. Babbage has presented Mossotti's theory under a mo- 

 dified form in note A : he says, " If matter be supposed to 

 consist of two sorts of particles, or rather centres of force, of 

 different orders of density, and if the particles of each sort re- 

 pel their own particles according to some given law, but at- 

 tract particles of the other kind according to another law, 

 then if we conceive only one particle of the denser kind to 

 exist, and an infinite number of the other kind, that single 

 particle will become the centre of a system surrounded by all 

 the others, which will form an atmosphere around it, denser 

 nearer the central body." 



Mr. Babbage observes, 1st. That one particle of the denser 

 kind will form around it an atmosphere of the other kind, 

 when such are present. 2nd. That a stream of the atmospheric 

 particles being added will increase its magnitude, and produce 

 undulations, which will continue till it is increased to a certain 

 extent, when it will begin to radiate. 3rd. " If the whole space 

 in which such a central particle is placed, is itself full of atmo- 

 spheric particles, then their density will increase in approaching 

 the central body." 4th. " If a stream of such particles were 

 directed towards the centre, they might produce throughout 

 the atmosphere vibrations, which would be transmitted from 

 it in all directions." 5th. " If two such central particles, with 

 their atmospheres, exist at a distance from each other, they 

 will be drawn together by a force depending on the difference 

 between the mutual repulsions." Pages 164, 165, 166. 



The following, extracted from my New Theory, nearly cor- 

 respond : 1st. The electric fluid and aethereal matter form at- 



