SECT, xiv.] MOLECULAR FORCES. 115 



as Sir David Brewster has discovered in the minute cavities 

 of various minerals, which occasionally causes these sub- 

 stances to explode with violence when under the hands of 

 the lapidary, but in general they seem to our senses to be 

 void ; yet, as it is inconceivable that the particles of matter 

 should act upon one another without some means of commu- 

 nication, there is every reason to presume that the interstices 

 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 required 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 distances ; and, as 

 they repel each other when they are inappreciably near, it 

 recently occurred to Professor Mossotti, of Pisa, that there 

 might be some intermediate 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 ofs matter 

 together. We are totally ignorant of the nature of elec- 

 tricity, but it is generally supposed to be an ethereal fluid 

 in the highest state of elasticity surrounding every particle 

 of matter ; and, as the earth and the atmosphere 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 mole- 

 cules of bodies to be surrounded by an atmosphere of the 



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