Srey.—On the Movements of Camphor on Water, 475 
are equal, each of the substances whose vapours we are operating with, is 
at such times subjected on all sides to a force tending to drive 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 tdm; but 
I wil 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 occurs whether in shape or area. 
Again, I place a small piece of camphor on this prepared surface, 
and puta 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, 
