478 Transactions.—Chemistry, 
movement, it occurred to me to try camphor itself. I placed a large piece of 
it upon water in a vessel closed from the air, and found, after the lapse of 
about four hours, that it was stationary, and that fresh pieces put therein 
would not move. I then took out the camphor and exposed the water 
freely'to the air for a short time, when I found that camphor would then 
describe very lively movements upon it. The same kind of effects are not 
produced if the camphor is kept wholly immersed in the water, not even if 
the time of contact is prolonged to a week. I further found that a water- 
surface, which has been rendered unfavourable for these movements by 
camphor, is also in a very unfavourable condition for the spread of oils 
thereon, so much so that some of them, when so placed, that is, of course, 
when used in small quantity, keep nearly to the drop form, 
The very pertinent facts are, then, now distinctly shown, that many 
vapours are obstructive to camphoric movements when condensed within or 
upon the upper stratum of any water on which camphor is moving, and 
that among these substances is camphor itself. Now we have already seen 
that all the substances just named above (and this includes camphor) are 
capable under certain circumstances of giving very decided and rapid move- 
ments to solid particles when they occupy a water-surface; and we have 
also seen that these vapours do not effect this directly by what I may here 
designate vapour force, but rather by surface modification. The conclusion, 
therefore, which one is led to by a consideration of all this is, that the 
movements of camphor in question are the effect of surface modification and 
modification which it produces itself. 
The analogy is, I hold, complete between resin upon water moving away 
from that which has been modified by vapour, and camphor upon water 
moving away from the water it has modified, except that we have one sub- 
stance less in the latter than in the former case—thus, camphor placed 
upon water gives up a part of its substance to the upper stratum thereof ; 
this part represents the vapours, whether of alcohol, ether, or camphor, 
which are resident in the clearing they have made amongst the particles of 
resin with which the water has been laden ; the remaining part of the 
camphor represents the resin which has been removed to make this clearing. 
Such is the theory which I submit to you as explanatory of the pheno- 
mena we have been observing. Ithink you will readily allow that it is at all 
events the most probable of any which you have now had for this purpose, 
and now it only remains for me to state to you what I conceive to be— 
1. The precise nature of the surface modification which I have 
eredited camphor with producing. 
2. The manner in which a surfaee so modified forces camphor to 
move. 
