184 Transactions. — Chemistnj, 



before, as I tldnh (tliis is, liowever, for measurement), and such 

 surface will not allow kerosene or turpentine to flow over it; i.e., a 

 drop of either put on keeps in nearly the drop form ; in pure 

 water they would flow over instantaneously. I have got the 

 surface to refuse olive oil even, a very searching oil though a 

 slow mover. This shows that such surface is a combination 

 of camphor with water ; and I am now enabled to fill up a 

 break you would observe in the continuity of my paper. I 

 now show how camphor forms some compound with water, 

 which will not allow oil to flow over it. This compound 

 is not camphor, because camphor is soluble in oil. I think it 

 is probably the hydrate. If it is the hydrate, the surface should, 

 by continued exposure, again rotate camphor, or allow oil to flow 

 over it ; and I find that two hours' exposure of a non-rotating 

 surface does restore to it the property of rotation. 

 II. That vapour does not necessarily repel, seems shown by the fact 

 that cork, on turpentine, or kerosene, is attracted by ammonia 

 vapour. Now, ammonia is a substance which, being rapidly 

 evolved — far more so than camphor — should repel cork on tur- 

 pentine strongly. (Camphor, I may say, and ether, and alcohol, 

 do repel cork on this liquid). 



Again : Turpentine vapour does not repel cork on turpentine, 

 but it repels cork on water ; and water offers more resistance to 

 the movements of substances swimming on it than to substances 

 swimming on turpentine. 



Clearly the idea that vapour in transit (molecular movement) 



can move masses of matter visibly to us, does not receive any 



support from such results as these. 



I am led to hold by researches here, and by thought on the matter, that 



the generally received idea that vapour exercises a direct repellent force, is 



entirely erroneous ; it appears to do so, but it in reality forms a compound 



with the liquid it appears to repel. A compound being lighter, or having 



greater diffusive power than the normal liquid, rolls like a wave away from 



the supply, and carries any dust mechanically with it, giving the apparent 



repulsive effect observed. 



Kepulsion by direct force of vapour is, I hold, an optical illusion, and 

 one which physicists should long since have exploded by force of pure 

 mathematical formulte, and not left it as a job for chemists. 



I shall in a future paper take the larger subject, that no kind of matter 

 can be visibly repelled while intercepting vapour in transit so long as a 

 common temperature is observed and the pressure is not notably irregular, 



