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Article XXIII. 



Oil the jForces ivhich regulate the Internal Constitution of 

 Bodies. By O. F. Mossotti. 



From a Memoir addressed to M. Plana, published separately, and communicated 

 by M. Faraday, Esq., D.C.L,, F.R.S., Src. 



Preliminary Remarks. 



1. X HE study of the phaenomena of nature has led philosophers to 

 consider bodies as being composed of molecules held in a state of fixed 

 equilibrium at a certain distance from each other. Such a state re- 

 quires that they should be endued with a certain action. Some pe- 

 culiarities of this action we are already able to assign, but its complete 

 characteristics are not yet well defined. 



As the resistance opposed by bodies to compression increases indefi- 

 nitely with the reduction of their volume, though their molecules have 

 not come into contact with each other, it shows that the force which they 

 exercise is repulsive at the least distances. At a distance greater than 

 these, but still imperceptible, it must vary with great rapidity, and be- 

 come attractive, in order that a steady equilibrium ot the molecules 

 may be possible ; and finally, when it has become perceptible, it must 

 decrease in the inverse ratio of the square of the distance, in order to 

 represent the universal attraction. The limits of the distance at which 

 the negative action becomes positive vary according to the temperature 

 and nature of the molecules, and determine whether the body which 

 they form be solid, liquid, or aeriform. 



There is a class of phaenomena, rather singular at first sight, in 

 which however it appears that nature designed, by separating the 

 forces which she employs, to present herself in all her simplicity. 

 Such are the phaenomena which constitute what we denominate 

 statical electricity. It is well known with what admirable facility 

 Franklin explained these phaenomena, by supposing that the mole- 

 cules of bodies are surrounded by a quantity of fluid or aether, the 

 atoms of which, while they repel each other, are attracted by the 

 molecules. It is known also how Coulomb subsequently proved that 

 the force with which the repulsion of atoms and the attraction of 

 the molecules are produced, is, like universal attraction, regulated by 

 the law of the inverse ratio of the square of the distance. Indeed, the 

 latter philosopher has substituted for the hypothesis of Franklin, which 

 is that generally followed in England, Germany, and Italy, another 

 hypothesis, in which a second fluid is supposed to perform the part as- 

 signed to matter in that of Franklin ; and this mode of explaining the 



