612 tECTUBE XLIX. 



The existence of a repulsive force, extending beyond the actual surface 

 of a material substance, being proved, it has been conjectured by some that 

 such a force, unconnected with any central atom, may be sufficient for pro- 

 ducing all the phenomena of matter. This representation may be admitted 

 without much difficulty, provided that it be allowed that the force becomes 

 infinite at or near the centre; but it has been sometimes supposed that it is 

 every where less than infinite, and conse(iuently that matter is not abso- 

 lutely impenetrable; such a supposition appears however to lead to the ne- 

 cessity of believing that the particles of matter must sometimes be annihilated, 

 which is not a very probable opinion. 



The magnitude of the repulsive force, by which the particles of any single 

 body are enabled to resist d^mpression, increases nearly in proportion to the 

 degree of compression, or to the decrease of the distances between the part- 

 icles. This is almost a necessary consequence of any primary law that 

 can be imagined, for the immediate actions of the particles: for instance, if 

 the repulsion increased either as the square or as the cube of the distance di- 

 minished, the effect of a double change of dimensions would ahvaj's be 

 nearly a double chaage of the repulsive force; that is, if an elastic substance 

 were compressed one thousandth part of its bulk, it would in either case re- 

 sist twice as much as if it were only compressed one two thousandth. 



It is obvious that if the particles of matter are possessed of a repulsive 

 force decreasing in any regular proportion Avith the increase of distance, 

 they can never remain at rest without the operation of some external pres- 

 sure, but will always retain a tendency to expand. This is the case of all 

 elastic fluids, the density of which is found to vary exactly as the compress- 

 ing force, whence it may be demonstrated, that the primary repulsive force 

 of the particles must increase in the same proportion as the distance de- 

 - creases. It follows also that this force can only be exerted between such 

 particles as are cither actually or very nearly in contact with each other; 

 since it requires no greater pressure, acting on a given surface, to retain a 

 gallon of air in the space of half a gallon, than to retain a pint in the space 

 of half a pint; which could not be, if the particles exercised a mutual re- 

 pulsion at all possible distances. 



