II. On Molecular Equilibrium. Part I. By the Rev. Philip Kelland, 

 M.A., Queens'" College, Cambridge; Professor of Mathematics in 

 the University of Edinburgh. 



[Read March 26, 1838.] 



INTRODUCTION. 



1. Whatever ideas may have been entertained of the nature of 

 forces at a distance from the centre of action, there appear to have 

 been no very definite notions current respecting molecular forces, till 

 within a few years from the present time. The obvious change in 

 the attractions of the different parts of a solid body, produced by sepa- 

 rating the particles by ever so small an interval ; the fact that the 

 attraction of cohesion when destroyed cannot be restored by any 

 ordinary pressure, indicated that the force which the particles exert on 

 each other in their positions of equilibrium, is of a nature totally distinct 

 from the appreciable attractions and repulsions at finite distances. New- 

 ton only threw out hints respecting the nature of forces of this kind, 

 never applying them, except in a popular manner in his Optics. One 

 kind of molecular force which he conjectures is that of the, particles 

 of air and the magnetic ones, Newton applies to calculation, but he 

 by no means supposes his hypothesis the correct one; on the contrary 

 he appears to entertain great doubts on the subject, for he concludes 

 his scholium by observing: "Whether elastic fluids do really consist 

 of particles so repelling each other, is a physical question. We have 

 demonstrated the properties of fluids consisting of particles of this kind, 

 that hence philosophers may take occasion to discuss that question." 

 Vol. VII. Part I. D 



