20 On the Hi/pothcsis of Gascons Repulsion. 



lion and unaffected vigour however mucli the air may be ex- 

 panded, would perhaps be thouglit hypercritical ; especially as 

 we have some analogy to it in the action of the magnet. It 

 would certainly be no difficult matter to show, that this pre- 

 tended analogy will by no means bear out the probability of 

 the hj-jiothesis. Objections however of this kind I shall not 

 stop to advance. My object will be to endeavour to prove 

 that this hypothesis, which Newton has found to agree with 

 one property of airs, is not consistent with other phaenomena, 



Newton thought it probable that, " as in algebra where af- 

 firmative quantities vanish and cease there negative ones begin, 

 so in mechanics where attraction ceaseth there a repulsive 

 virtue ought to succeed." In other words, Newton conceived 

 that there are distances within which particles may attract 

 each other, but without which they repel. No one certainly 

 will deny, but that repulsion, physically speaking, is e^jually 

 as probable as attraction ; and that, if the one exists, no reason 

 appears why the other should not. If, however, a mere se- 

 paration of the component parts of a body, to a greater di- 

 stance from each other, be sufficient to change that mutually 

 attractive force which they are supposed to have when nearly 

 in contact into repulsion, then instead of distant bodies attract- 

 ing one another as they are found to do, they ought to repel, 

 in consequence of the antipathy which the distance lias occa- 

 sioned in the particles of one body for those of the other. Par- 

 ticles of any one body likewise, which are within their com- 

 mon sphere of attraction, should mutually attract each other, 

 and those which are without that sphere should reciprocally 

 repel ; so that by this theory a body would be kept entire by 

 the excess of the attraction of the nearer above the repulsion 

 of the more remote particles. Hence, if a part of the body 

 be removed to a greater distance from its surface than the 

 sphere of attraction of the nearest superficial particles extends, 

 it would no longer be attracted, or have a tendency to approach 

 the body of which it formed a part, but would endeavour to 

 recede from it as far as possible ; which is contrary to ex- 

 perience. 



If, to avoid this difficulty, it be urged that the repelling force 

 exists only when the elementary parts of a body ai-e singly se- 

 parated to greater distances than their individual sjiheres of 

 attraction extend ; and that in other cases the adjacent particles 

 attract not merely each other, but also those particles that are 

 without their sphere of attraction, then it will follow, that if 

 there be two clusters of particles A and B, and the particles 

 of A, first supposed in their sphere of repulsion, approach each 

 other whilst the clusters themselves retain the snme distance, 



the 



