SECT. XIV. MOLECULAR FORCES. 97 



nication, tnere is eveiy reason to presume that the in- 

 terstices of material substances contain a portion of that 

 subtle ethereal and elastic fluid with which the regions 

 of space are replete. 



Substances compressed by a sufficient force, are said 

 to be more or less elastic according to the facility with 

 which they regain their bulk or volume when the 

 pressure is removed ; a property which depends upon 

 the repulsive force of their particles, and the effort re- 

 quired to compress the substance is a measure of the 

 intensity of that repulsive force which varies with the 

 nature of the substance. 



By the laws of gravitation the particles of matter 

 attract one another when separated by sensible dis- 

 tances; and as they repel each other when they are 

 inappreciably near, it recently occurred to Professor 

 Mossotti of Pisa, that there might be some intermedi- 

 ate distance at which the particles might neither attract 

 nor repel one another, but remain balanced in that 

 stable equilibrium which they are found to maintain in 

 every material substance solid and fluid. 



It has long been a hypothesis among philosophers 

 that electricity is the agent which binds the particles of 

 matter together. We are totally ignorant of the nature 

 of electricity, but it is generally supposed to be an ethe- 

 real fluid in the highest state of elasticity surrounding 

 every particle of matter ; and as the earth and the at- 

 mosphere are replete with it in a latent state, there is 

 every reason to believe that it is unbounded, filling the 

 regions of space. 



The celebrated Franklin was the first who explained 

 the phenomena of electricity in repose, by supposing 

 the molecules of bodies to be surrounded by an atmos- 

 phere of the electric fluid ; and that while the electric 

 atoms repel one another, they are attracted by the ma- 

 terial molecules of the body. These forces of attraction 

 and repulsion were afterward proved by Coulomb to 

 vary inversely as the squares of the distance. The 

 hypothesis of Franklin waa reduced to a mathematical 

 theory by JEpinus, and the most refined analysis has 

 been employed by the Baron Poisson in explanation of 

 electric phenomena. Still these philosophers were un- 



