84 On Cohesmi. 



themselves (for every particle added increases the attraction of 

 the whole), and that the attraction of the whole is an aggregate 

 of the attractions of its particles. But the particles of hodies being 

 infinitely minute, the spaces in which their individual attractions 

 are sensible must be infinitely small, and at sensible distances 

 these attractions must become insensible. The attraction of a 

 mass therefore at a sensible distance is an aggregate of indivi- 

 dually insensible attractions ; but at an insensible distance it be- 

 comes an aggregate of sensible attractions; — a conclusion which 

 is supported by actual experiment : for if two rough surfaces be 

 presented to one another, the attraction is insensible, the distance 

 of their particles being sensible (and the aggregate not sufficiently 

 great to render the individual attractions sensible) ; hut if the di- 

 stance be rendered (by polishing)insensible, the attraction imme- 

 diately becomes sensible. The particles of bodies therefore, when 

 placed at insensible distances, exercise sensible attractions in vir- 

 tue of the attraction of gravitation, and at sensible distances this 

 attraction (unless the, masses be immensely large) ceases. The 

 attraction of cohesion follows precisely the same laws: — may it 

 not then be fairly inferred, that these attractions are one and the 

 same ? 



If the primary particles of bodies be allowed to posses? the 

 power of attraction, it may be inferred on similar grounds, that 

 the particles of which they are composed are likewise en(lued 

 with it ; we must therefore allow them cohesion, and that their 

 cohesion and attraction is more powerful than that of the primary 

 particles themselves: we must likewise conclude the form of a 

 primary particle to be spherical. 



It being admitted that the attraction of cohesion and the at- 

 traction of gravity are the same, it follows from a moment's con- 

 sideration that the particles of different bodies must differ in size 

 and in density. 



Let a primary particle A containing a quantity of matter (fl) 

 be presented to another, B, containing a quantity of matter (//), 

 and let the attraction 'at the surface of A be greater than that at 



the surface of B; i, e. let ^B x a be greater than ^A x I, 

 and let the contact of A and B be so minute that some of the 

 secflndary particles ofD may be within the sphere of the attrac- 

 tion of those of A. Then, the attraction of the particles of A being 

 greater than the attraction of the particles of B, it will also be 

 greater than their cohesion ; and their cohesion being destroyed, 

 the attraction of the whole mass A being greater than that of B, 

 these secondary particles of B will leave it, and form round A ; 

 and the operation will be continued till the two are formed into 

 one, whilst every secondary particle exerting a similar attraction, 



the 



