On the Motions of Camphor and Odorani Bodies. 35 



always retain a flight degree of motion, by which they refemble groupes of capillary eels, 

 that move fpontaneoufly, till they are entirely confumed by evaporation ; this motion de- 

 pends on the flow expanfion of the volatile oil of camphor which takes place at the furface of 

 the water, in proportion as that which remains is evaporated, as we have already mentioned. 

 At firft I entertained doubts whether the motions of the camphor upon water were fuf- 

 pended by the expanfion of olive oil, or any other oleaginous fubftance, merely becaufe 

 that of the camphor, being more denfe, did not poflefs the faculty of expanding as quick 

 as the liquid oils. To elucidate this point, I made the following experiments : I melted a 

 fmall quantity of camphor in a fpoon by the flame of a candle, and poured it upon hot 

 water, on the furface of which a drop of olive had previoufly expanded : in its melted ftate 

 it was not at all capable of extending, and expelling the olive oil ; ftill lefs of giving motion 

 to farinaceous matter. I next threw fome pieces of the inflamed camphor on the furface 

 of cold water ; and they moved extremely well. As I fuppofed that it was the heat of the- 

 inflammation, which by melting the oil of the camphor obliged it to continue to expand,, 

 I poured on this water fome drops of olive oil ; the motion of the camphor then imme- 

 diately ceafed, and did not recommence, though the fubftance continued to burn. Hence it 

 muft with certainty be concluded, that the oil of camphor has lefs attra£lion of furface foe 

 water than olive oil, or feveral other oleaginous fubftances, fuch as the flour of wheat. 



Camphor, well heated, and fuming^ as Venturi has obferved, being brought near very 

 light bodies floating on the furface of water, fuch, for inftance, as pieces of gold or filver 

 leaf, exerts upon them a repulfive force, exaftly the fame as when it is thrown upon cold 

 water; and, according to him, this effeft is owing totheelaftic fluid, which ftrikes againft 

 thofe bodies: this notion alfo occurred to Prevoft. For my own part, I think this efi^e£t 

 is produced only by an oil which expands upon the water : the oil of camphor, reduced to 

 vapour by heat, when it comes in conta£l with water, expands on the furface, and thus 

 imparts a motion to the bodies it meets with, and feems to repel them.- In h€t, if we at- 

 tentively obferve the furface of the water around the floating body which is moved, it will 

 be feen to be covered with a fmall very thin and whitlfli film (of varnifh) which is, doubt- 

 Icfs, a proof that the oil of the camphor, when volatilifed. Is extended over the water, and 

 by cooling depofits a fine incruftation. 



It is not, therefore, proved by any of thefe experiments that the atmofphere, which is 

 formed by the odour of the bodies, poflrefl"es, as Prevoft pretends, an expanflve power 

 capable of being rendered perceptible. Thofe bodies- which are moft effe£lually odorant^ 

 that is to fay, furrounded, like the others, by an atmofphere of odoriferous emanations^ 

 but which are not mixed with a volatile oil, do not caufe any repulfion in bodies floating in 

 water, however near they may be brought to each other. 



And if the mere emanation and projeftion of an elaftic odoriferous fluid were the only 

 eaufes of the motions of camphor and other odoriferous bodies by water, thefe motions 

 would take place on throwing in any one of fuch bodies ; but if, for example, even the 

 fmalleft piece of camphor be dropped upon water with a confined furface, the motions are 

 not produeed ; it is therefore evident that they are caufed by the furface of the water alone^ 

 4 uSccoufit 



