PROFESSOR KELLAND, ON MOLECULAR EQUILIBRIUM. 59 



particle estimated in the direction of this line, will be different from 

 the force in a plane perpendicular to it, not only in value, but also in 

 form. 



For the supposition of contact between the material particles amounts 

 to that of exclusion of caloric particles, and consequently we cannot 

 estimate the action of each particle on every other, as though these 

 two were the only ones of the system, but must add or subtract from 

 that action a force due to the caloric displaced at the point of junction ; 

 and further, the repulsion of the caloric surrounding a particle, must 

 be diminished in the direction of the line joining the centres, on ac- 

 count of the quantity displaced by the neighbouring particle. The two 

 sets of forces will therefore be totally different in form in the two 

 directions. In that joining the centres of the particles, the variation 

 of the attraction for a variation of q as well as for a variation of a, 

 will be very considerable, whereas in a perpendicular direction both 

 variations will be small. But besides this, it will be seen that the 



M* — qMP 



term which in Art. 29. completely destroyed g , being 



a term arising from the displaced caloric, will not now be sufficient 

 to destroy it on account of the accompanying particle, consequently 

 a very small attraction varying inversely as the square of the distance 

 will remain. This attraction cannot have a sensible value as compared 

 with the other terms when the distance is small; but when the distance 

 is finite, the rapid diminution of e~ aa renders the other terms very 

 much smaller than this, and at a considerable distance this term is the 

 only one sensible : at such distances then, the force varies inversely as 

 the square of the distance. Thus all the known laws, as well of at- 

 traction as of cohesion, are explained by the Newtonian hypothesis. 



Queens' College, 

 March 10, 1838. 



Note (a). Let A be the centre of the attracting, B of the attracted particle AB = a, 



AQ = p, AC=R the radius of any sphere, V= the volume of B = — angle QAM=<j>. 



3 



H2 



