Skey. — On the Movements of Camphor on Water, 47S 



are equal, eacli of the substances whose vapours we are operatmg with, is 

 at such times subjected on all sides to a force tending to diive it in, that is, 

 towards its centre ; a force which, as it cannot be persistently equal around 

 it, will certainly move it from its normal position. 



This is, I allow, a conclusion which one is at first inclined to form ; but 

 I will now show to you an extension of this experiment yielding results 

 which will, I think, at once prevent anyone previously so inclined from this 

 conclusion. 



The camphor is now only one-sixth of an inch above the water, and the 

 diameter of the cleared space below it is about half an inch ; I now lower 

 it to within one-fortieth of an inch of the water, but you observe that the 

 area of cleared space is not perceptibly increased, thereby showing that 

 this is very closely upon the maximum of that which can be got by placing 

 the camphor at an infinitesimal distance from the water. I now allow it 

 the slightest contact with the water which I possibly can, and you observe 

 that there is instantly a very large increase of cleared space, whose 

 diameter is certainly not less than four inches, representing, therefore, an 

 area no less than sixty-four times that which we had before. 



Here, then we have, in one moment, an accession to our knowledge of a 

 kind which teaches us that, whatever the direct radiation of camphor vapour 

 may have to do with the production of the cleared space last got, there is 

 some reaction of camphor with water of quite a different nature which has 

 very much more to do with it ; so great, indeed, is the effect produced by 

 the merest contact as compared with that obtained by suspension in the most 

 favourable position, that it really becomes a moot point whether any space 

 at all is cleared by the direct impingement of this vapour on the water 

 surface. 



To settle this point by a demonstration I now reproduce certain experi- 

 ments of mine : — This small sphere of camphor I suspend over water (pre- 

 pared as above) within one-sixth of an inch of its surface, and across 

 the cleared space produced, close to the camphor and closer to the water 

 than the camphor is, I place this thin bar; now this clearing should have 

 its shape materially altered, and its area much curtailed if it has been 

 produced by the mere impingement of vapour on water; but you cannot see 

 that any variation occm's whether in shape or area. 



Again, I place a small piece of camphor on this prepared surface, 

 and put a wide bar close to one side of it and very near to the water ; 

 now, action and reaction being equal there should occur a marked 

 recession of the camphor from the bar if the evaporation theory is correct, 

 for in the direction of this bar is the greatest resistance to the escaping 

 vapour ; but you cannot observe that anything of this kind happens. 



