344 Note by M. Ampere on Heat and Light 



or more of these molecules unite to form more compound 

 ones. 



Mechanical forces can only separate the particles: the force 

 resulting from the vibration of the atoms can separate the 

 more compound molecule of a solid substance into more sim- 

 ple ones, such as those which exist in a liquid or in a gas. 

 Chemical forces alone can separate ulteriorly these last mole- 

 cules. For example, in the detonation of the mixture of one 

 volume of oxygen with two of hydrogen, from which result 

 two volumes of aqueous vapour, reduced to the original tem- 

 perature, every molecule of oxygen is divided into two, and 

 the atoms of each of these halves unite to the atoms of a mo- 

 lecule of hydrogen to form a molecule of water. 



This division of molecules by chemical forces results from 

 a principle which I established in a memoir printed in 1814, 

 in the Annates des Mines, namely, that in equal volumes of 

 any gas or vapour whatever, under the same pressure and at 

 the same temperature, are contained the same number of 

 molecules. 



With regard to atoms, the only property which I think can 

 with certainty be attributed to them is that of being abso- 

 lutely indivisible, so that although space be infinitely divisible, 

 matter cannot be so, for when the division is conceived to 

 have arrived at the atoms, every further division would of 

 necessity take place in the intervening empty spaces*. Enter- 

 taining such views of this subject, I distinguish molecu- 

 lar from atomic vibrations. In the first the molecules vi- 

 brate collectively in approaching to and receding from one 

 another alternately ; and whether they so vibrate or are at 

 rest, the atoms of every molecule can, and, in fact, always do, 

 vibrate in alternately approaching and receding from one 

 another, without ceasing to belong to the same molecule. 

 These last I call atomic vibrations. 



It is to molecular vibrations, and their propagation through 

 ambient mediums, that I attribute all the phenomena of 

 sound; to atomic vibrations, and their propagation through 

 the aether, I attribute all the phenomena of heat and light. 

 Vibratory motion not being possible except around a state 

 of stable equilibrium between opposed forces, the atomic 

 vibrations necessarily suppose the existence of a repulsive 

 force in equilibrium with an attractive force, these two forces 

 acting at the same time between two atoms, so as to allow the 

 possibility of a stable equilibrium between these two forces ; 

 which circumstance will necessarily cause the repulsive force 

 to increase or decrease with greater rapidity than the attrac- 



[* On this subject see Phil. Mag., first series, vol. lxii. p. 360. and vol. 

 lxiii. p. 372.- Edit.] 



