474 Transactions.—Chemistry. 
and the more so when, on enquiring into this, he learns that no one has yet 
published anything in explanation of this phenomenon which is backed 
either with any kind of authority or, what is more, by a weight of evidence 
sufficient to recommend it for his unqualified belief. 
It was just under these incentives to research that, a little while ago, I 
commenced investigating this phenomenon, and with the additional one of 
ultimately finding something in common between it and that of the motion 
of minute particles in certain liquids—one known by the appellation of 
“ Browinian movements "—the Pedetic movements of Prof. Jevons. 
After I had made a great number of experiments with camphor, how- 
ever, I could find nothing which gave any proof in favour of a common origin 
for the two phenomena. Neither could I find anything in support of the 
theory popularly assigned for the explanation of that exhibited by camphor, 
but instead, evidence of a very decided character, pointing, as I think, 
very clearly to quite a different origin for it than that which is assigned 
y the theory in question. This I now ask leave to submit to your 
inspection, and, if you will allow me, I will do this in the same order, or 
nearly so, in which it was educed. 
First, I will remind you what this theory is, which is thus endorsed by 
popular opinion. Itis based upon the fact that camphor gives off vapour 
at common temperatures, and it is to the unequal impingement of this 
vapour upon the water around it that the movements in question are 
ascribed, the camphor being held, as I suppose, to move in the direction of 
least evaporation. 
Now this does, I allow, appear at first thought quite explanatory to 
anyone who will observe the effect which camphor vapour, or vapours, 
generally have upon water, the surface of which is prepared so as to 
indicate any modification it thereby undergoes. Such a surface, in the case 
of water, is easily got by dredging a little very finely-powdered resin evenly 
upon it.” 
Camphor suspended close to a surface of this kind produces, as you see, 
an instantaneous recession of the resinous particles from the point imme- 
diately under it; the same effect is also produced by those substances 
generally which give off vapour in suitable quantity at the temperature at 
which they are used; for instance, alcohol or ether. 
It does, indeed, appear from this, that the popular theory which we are 
attacking is, after all, correct. One sees the resin quickly dashed away from 
the camphor, etc., and in consequence conclude that, as action and reaction 
* This surface so well indicates (by the displacement of resin) the presence of oily 
matters that these can readily be detected, as they escape from the finger applied thereto, 
pyen immediately after a thorough wash. 
