AMADEOAVOGADRO i8i 



oxygen, has a volume equal to the sum of the two constituent gases, 

 that is to say, double that of each of them. Thus in all these cases 

 there must be a division of the molecule into two ; but it is possible 

 that in other cases the division might be into four, eight, &c. The 

 possibility of this division of compound molecules might have been 

 conjectured a priori; for otherwise the integral molecules of bodies 

 composed of several substances with a relatively large number of 

 molecules, would come to have a mass excessive in comparison with 

 the molecules of simple substances. We might therefore imagine that 

 nature had some means of bringing them back to the order of the 

 latter, and the facts have pointed out to us the existence of such 

 means. Besides, there is another consideration which would seem to 

 make us admit in some cases the division in question ; for how could 

 one otherwise conceive a real combination between two gaseous sub- 

 stances uniting in equal volumes without condensation, such as takes 

 place in the formation of nitrous gas? Supposing the molecules 

 to remain at such a distance that the mutual attraction of those of each 

 gas could not be exercised, we cannot imagine that a new attraction 

 could take place between the molecules of one gas and those of the 

 other. But on the hypothesis of division of the molecule, it is easy 

 to see that the combination really reduces two different molecules to 

 one, and that there would be contraction by the whole volume of one 

 of the gases if each compound molecule did not split up into two 

 molecules of the same nature. M. Gay-Lussac clearly saw that, 

 according to the facts, the diminution of volume on the combination 

 of gases cannot represent the approximation of their elementary mole- 

 cules. The division of molecules on combination explains to us how 

 these two things may be made independent of each other. 



III. 



Dalton, on arbitrary suppositions as to the most likely relative 

 number of molecules in compounds, has endeavoured to fix ratios be- 

 tween the masses of the molecules of simple substances. Our hypoth- 

 esis, supposing it well founded, puts us in a position to confirm or 

 rectify his results from precise data, and, above all, to assign the 

 magnitude of compound molecules according to the volumes of the 

 gaseous compounds, which depend partly on the division of mole- 

 cules entirely unsuspected by this physicist. 



