18 
MB, J. J. WATERSTOB OB THE PHYSICS OF MEDIA COMPOSED OF 
various proportions, forming etherine, ceten, elaen, &c., all of which are isomeric hut 
have different specific gravities as vapours. These the chemist is unable to form 
directly; they are organic products and show a great molecular capability that is 
undoubtedly common to all bodies. 
There has certainly as yet been no recognised example of a simple element appearing 
in the gaseous form with two specific gravities, but it would be rash to affirm that 
such was either impossible or absurd. Indeed, chlorine, bromine, iodine, and fluorine 
are so similar in their chemical qualities that it is not very unlikely they may be 
examples of isomeric combinations of one base in which condensation of atomic volume 
takes place simultaneously with increment of atomic mass. In the hydrocarburets, 
on the other hand, there is little, if any, condensation of atomic volume, their specific 
gravity in the liquid form being all nearly the same. 
A strong argument in favour of the physical origin of the law of volumes is to 
be obtained from the combination of acids with ether. Some of these rise up into 
vapour in the same state of chemical union as when liquid, while others quite similar 
are decomposed in the act of rising and occupy double the volume of the others. 
Even those that are fully combined when they first rise, by an increase of temperature 
not very considerable, are decomposed and immediately assume a double volume. 
Oxalic and nitrous ethers are examples of the last kind. Sulphate and nitrate of 
pyroxilic ether are examples of disunion in the act of rising. 
If the hypothetical law of volumes is true in all cases, we should have to distinguish 
between atomic weight and combining proportion. Thus, if the atomic weight of 
oxygen is 1 (or specific gravity of gas), its combining proportions are Ir, 1, 1^, 2, 
2-^, 3, 3| (?). If the atomic weight of hydrogen is 1, its ascertained combining 
proportions are 1, 1-|, 2, 3, 4, 5, 6, 8, 9, 16. If the atomic weight of nitrogen is 1, 
its combining proportions are ^ and 1. The same for chlorine is 1, ll?, 2, 2^; 
for bromine they are 1, 1^; for iodine, 1, 1^; for arsenic, 1; for sulphur, 
; for phosphorus, &c. These are necessarily derived from the specific gravity 
of the simple gases and of their compounds. 
The labours of Dumas, Mitscherlich, Regnault, and Bineau, have extended the 
list of gases and vapours, whose specific gravities have been accurately measured, to 
nearly 150. Such determinations throw a light upon the atomic constitution of 
compounds which it is impossible to obtain from their mere chemical analysis, and 
form an important guide to theoretical discussion, when the arithmetic of volumes is 
properly applied. 
Section III.— On the Phenomena that Attend the Condensing and Dilating 
of Media, and the Mechanical Value of their Molecular Vis Viva. 
§ 16. In the first section a distinct idea of the elastic force of the medium was 
obtained by viewing it as a rapid succession of impacts on the lower surface of a 
