474 Transactions. — Chemistry. 



and the more so •when, on enquiring into this, he learns that no one has yet 

 pubHshed 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 experim^ts 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 omgin for it than that which is assigned 

 by the theory in question. This I now ask leave to submit to your 

 inspection, and, if you will aUow 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. It is 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 weU 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, 

 eyen immediately after a thorough wash. 



