THE INTERNAL CONSTITUTION OF BODIES. 469 



the third gives, for the determination of r, 



, . — ar 



ffy^-i^ + q)^ ^ "^^/^' — -(ff-y) v^x."-^i, = o. 



If the density of the aether into which the molecules are plunged, or 

 the quantity go, becomes greater, the density q given by the equation 

 (6) will increase also ; that value of r which will satisfy the foregoing 

 equation will consequently become greater, and the molecules Avill fix 

 themselves in equilibrium at a greater distance. We see in this result 

 that the aether performs the functions of caloric, and that it is to its 

 greater or less density we are to ascribe the temperature and volume 

 of the bodj'. For what else, in fact, is an increase or diminution of 

 temperature in respect to a body, than a new state in which its mole- 

 cules, placed in equilibrium, form, in consequence of their being more 

 or less widely separated, a greater or less volume. It has been known 

 to philosophers since the time of Galileo, who was the first that clearly 

 pointed out this difi'erence, that we are not to confound the sensation 

 which we experience while this new arrangement of the molecules of 

 our body is taking place, with the motion by which it is produced. 



NOTE. 



[The readers of this Memoir will doubtless be interested in referring 

 to Dr. Roget's " Treatise on Electricity " in the Library of Useful Know- 

 ledge, published March 15th, 1828; the following passage from which 

 ■yvas noticed with reference to M. Mossotti's views, by Prof. Faraday in 

 his lecture at the Royal Institution, Jan. 20th of the present year. — 

 Edit.] 



" (239.) It is a great though a common error to imagine, that the 

 condition assumed by iEpinus, namely that the particles of matter when 

 devoid of electricity repel one another, is in opposition to the law of 

 universal gravitation established by the researches of Newton ; for this 

 law applies, in every instance to which inquirj' has extended, to matter 

 in its ordinarj' state ; that is, comljined with a certain proportion of 

 electric fluid. By supposing, indeed, that the mutual repulsive action 

 between the particles of matter is, by a very small quantity, less than 

 that between the particles of the electric fluid, a small balance would 

 be left in favour of the attraction of neutral bodies for one another, 

 which might constitute the very force which operates under the name 

 of gravitation ; and thus both classes of phaenomena may be included 

 in the same law." 



