OF GASEOUS BODIES. 119 



If the self- repulsive force of caloric in these 

 compound gases were not counteracted by an 

 attraction between their particles and thermal 

 aether, their elastic force would be greater than 

 that of hydrogen in proportion to the greater 

 amount of their latent caloric. 



This conclusion is rigorous ; and it is so im- 

 portant in its bearing upon the whole science of 

 chemistry and physics, that I have dwelt upon 

 it even at the hazard of repetition, with a hope 

 that by presenting the operation of the same 

 principle in different points of view, it might be 

 rendered clear and intelligible to the most ordi- 

 nary capacity. It explains why the expansive 

 force of steam is greater, other things being equal, 

 in proportion as the quantity of water employed 

 in its generation is less ; a thorough comprehen- 

 sion of which is destined to effect an immense 

 saving of fuel. 



The law by which the elastic force of aethereal 

 matter is counteracted by the mutual affinity be- 

 tween it and ponderable matter, is still more strik- 

 ingly illustrated by the changes which are pro- 

 duced in the statical and dynamical properties of 

 hydrogen and sulphur, oxygen and nitrogen, 

 chlorine and nitrogen, with some others. 



It was before noticed that the specific gravity of 

 sulphur vapour as determined by the experiments 

 of Mitscherlich, is 6*666, which is about 96 times 

 the specific gravity of hydrogen gas : and it re- 



