THE INTERNAL CONSTITUTION OF BODIES. 469 
the third gives, for the determination of r, 
—ar 
gvi(at ee? ee —(g—y) viat =o. 
If the density of the «ther into which the molecules are plunged, or 
the quantity ¢., becomes greater, the density q given by the equation 
(6) will inerease also; that value of r which will satisfy the foregoing 
equation will consequently become greater, and the molecules will fix 
themselves in equilibrium at a greater distance. We see in this result 
that the zther 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 body. 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 difference, 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 
was noticed with reference to M. Mossotti’s views, by Prof. Faraday in 
his lecture at the Royal Institution, Jan. 20th of the present year.— 
Epit. | 
*¢(239.) It is a great though a common error to imagine, that the 
condition assumed by /Epinus, 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 inquiry has extended, to matter 
in its ordinary state; that is, combined 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 phenomena may be included 
in the same law,” 
