34 Dr. W. C. Henry's Reniarfo on the 



conception without being aware that it had been previously 

 entertained by others. These distinguished chemists do not, 

 however, concur with Ampere in regarding it in the light 

 merely of an hypothesis, but conceive that it is strictly deriv- 

 able from the well-known law of Mariotte, and from the si- 

 milar relations of gaseous bodies to heat. They have there- 

 fore made the first of the above propositions the basis of their 

 peculiar views on atomic combination, and have certainly suc- 

 ceeded in proving that the second and more important pro- 

 position flows from the first in direct logical sequence. It is 

 therefore necessary to examine, with peculiar care, the grounds 

 upon which the major term is supposed to rest. 



The law of Mariotte, that in all elastic fluids the volumes 

 vary inversely as the compressing forces, will be found to 

 warrant no inference as to the number of atoms existing in 

 a given volume of the different gases. It is derived from 

 the law of variation observed by the repulsive forces which 

 actuate the molecules of elastic fluids, not from the nume- 

 rical aggregation of atoms in space. Newton has demon- 

 strated (Princ., Lib. II. Pr. xxiii.) " that particles flying 

 from each other with forces that are reciprocally propor- 

 tional to the distances of their centres, compose an elastic 

 fluid whose density is as the compression," Now this is the 

 law of Mariotte, which is hence independent of all elements 

 other than repulsive forces, varying inversely as the atomic 

 distances or diameters. Whatever be the comparative di- 

 stances of the particles of two gases A and B under any given 

 pressure, the same for both, there must, in conformity with 

 the law of Newton, be an equal diminution of their bulk on 

 equal increments of pressure. For illustration, let us suppose 

 the atoms of A to be at double the distance that exists be- 

 tween the atoms of B under the pressure of one atmosphere. 

 Let the two gases be subjected to the pressure of an additional 

 atmosphere. Then, since the molecular forces in both vary 

 according to the same law, both gases will be alike reduced to 

 half their original volume. But the number of atoms of B is 

 eight times that of A. Hence it is manifest that the law of 

 Mariotte has no reference whatever to the numerical relations 

 of atoms in the different gases. 



2nd, The argument founded on the equal expansion of the 

 gases by heat, does not appear to be possessed of greater co- 

 gency. In the first place, it is consistent with the best recent 

 experiments, as will be shown hereafter, that equal increments 

 of absolute heat do not produce equal dilatations of volume in 

 the different gases, and that this relation can only be correctly 

 predicated of equal increments of temperature. Now there seems 



