36 ON THE ABSOEPTION AND EADIATION OE HEAT BY GASES AND VAPOIJES. 
facility through the ether, but the ease of motion which these molecules enjoy must 
facilitate their mutual collision. Their motion, instead of being expended on the ether 
which exists between them, and communicated by it to the external ether, is in great 
part transferred directly from particle to particle, or in other words, is freely conducted. 
When a molecule of alum, on the contrary, approaches a neighbour molecule, it pro- 
duces a swell in the intervening ether, which swell is in part transmitted, not to the 
molecules, but to the general ether of space, and thus lost as regards conduction. This 
lateral waste prevents the motion from penetrating the alum to any great extent, and 
the substance is what we call a bad conductor*. 
Such considerations as these could hardly occur without carrying the mind to the 
kindred question of electric conduction ; but the speculations have been pursued suffi- 
ciently far for the present, and must now abide the judgment of those competent to 
decide whether they are the mere emanations of fancy, or a fair application of principles 
which are acknowledged to be secure. 
The present paper, I may remark, embraces only the first section of these researches. 
* lu the above considerations regarding conduction, I have limited myself to the illustration furnished 
by two compound bodies, but the elementary atoms also differ among themselves as regards their powers of 
accepting motion from the ether and of communicating motion to it. I should infer, for example, that the 
atoms of platinum encounter more resistance in moving through the ether than the atoms of silver. It is 
needless to say that the physical texture of a substance also has a great influence. 
