82 On Cohesion. 



than its gravity. Now attraction being known to exist in propor- 

 tion to the quantity of matter, and the attraction of gravity being 

 exerted between a comparatively small and an immensely large 

 aggregate of matter, whilst that of cohesion only exists between 

 small aggregates; it seemingly implies that a less attraction is 

 more powerful than a greater. In answer to this it may be stated, 

 that gravity being exerted at exceedingly great, whilst cohesion 

 onlv exists at insensibly small distances, the energy of the one 

 can be no fair criterion to judge of that of the other. In the sub- 

 sequent part of this paper it will be shown that gravity is an ag- 

 gregate of attractions which would be individually insensible ; 

 whilst cohesion is an aggregate of individually sensible attrac- 

 tions. Now of the two masses between which gravity is exerted, 

 one (the earth) being infinitely greater than either of those be- 

 tween which cohesion exists, it follows that the aggregate of in- 

 sensihle attractions is infinitely greater than the aggregate of sen- 

 sible attractions. But this by no means precludes the possibility 

 of the latter being infinitely stronger than the former: besides, it 

 must be recollected that the cohesion of one particle is not merely 

 the effect of the attraction of another, — every particle being sphe- 

 rical, is in contact with eighteen others ; every effort therefore to 

 remove a single particle vvill be resisted in a greater or less de- 

 gree by at least nine other particles. 



Another objection that has been urged is, that the power of 

 cohesion diminishes much faster than the square of the distance : 

 some, indeed, have gone so far as to assert, that it diminishes as 

 the cube of the distance. By what means these conclusions are 

 obtained 1 know not ; except it be by approaching the particles 

 of bodies, and observing mechanically their attractions at different 

 distances. The power of cohesion acting only between particles, 

 and these particles being insensibly small, can but extend its in- 

 fluence to insensibly small distances; and to attempt to measure 

 the sensible decrease of a power which at sensible distances is in- 

 sensible, is attempting to divide mechanically an insensibly small 

 space ; — the result of such an attempt cannot certainly be urged 

 as an argument. 



It may again be objected, by those who believe in the ex- 

 istence of repulsion between the particles of matter, that by this 

 hypothesis no such power is accounted for. The existence of re- 

 pulsion is not, however, by any means demonstrated ; and all the 

 experiments adduced in favour of it (with the exception of those 

 connected with electricity and magnetism) may be accounted for 

 without having recourse to such a power. 



The three principal objections which apply generally to this 

 hypothesis having been answered, I shall consider it admitted, 

 that the attraction of gravitation and the attraction of cohesion 

 may be the same, and proceed to prove that they are so. 



