414 Mr. C. Tomlinson on the Motions of Camphor 



of sodium with most of the metals also rotate on mercury, or on 

 a thin plate of water on mercury. 



19. In 1825 the brothers Weber 21 , in noticing Franklin's ex- 

 periment (6), reiterate the fact that a downy feather smeared 

 with oil rotates on water, and express their opiuion that the mo- 

 tions of camphor and of various other bodies on water still remain 

 to be accounted for by a satisfactory theory. 



20. In 1833 Matteucci 22 states that raspings of cork steeped 

 in ether rotate on the surface of water, and continue to do so as 

 long as the surface is supplied with ether, as by conducting a 

 thread from the ether bottle to the surface. His conclusion 

 is that it is to the currents of volatile substances that the mo- 

 tions are due. 



21. In 1841 Dutrochet 23 described the following experi- 

 ment : — If cork be steeped in a solution of caustic alkali and 

 dried and then be placed on water, the solution is projected 

 strongly from the cork, and this moves in the opposite direction. 

 " This motion of the cork is evidently the effect of recoil produced 

 by the repulsion which the solid alkali contained in the cork exerts 

 on its own solution. It is very probable that this repulsion is elec- 

 trical, and arises from the fact that the solid body dissolved has a 

 similar electricity to that of the solution. However this may be, 

 the fact of the reciprocal repulsion of the soluble body and of the 

 aqueous solution is certain, and it is to this repulsion that we 

 may attribute the motion that takes place at the surface of water 

 of all floating bodies that dissolve in it. This occurs not only 

 in the case of alkalies, acids, and salts, but in gum resins, such 

 as opium, aloes, fee.'" 24 . 



22. In 1841 Messrs. Joly and Boisgiraud 25 bring before the 



21 Wellenlehre. Leipzig, 1825. 



22 Ann. de Chirn. et de Phys. vol. liii. p. 216. 



23 Comptes Rendus, vol. xii. p. 2. 



u This experiment is evidently based on Prevost's experiments (note 15 ), 

 intended to show that almost all liquids are each susceptible of repelling 

 all others or of being repelled by them ; that is, if a liquid be made to cover 

 a glass plate, and a drop of another liquid properly selected be placed on 

 the film, the latter will be driven away and the second will occupv its place. 

 Thus 



Ether repels Alcohol. 



Alcohol „ Essential oil of peppermint. 



Oil of peppermint „ Oil of bergamot. 



Oil of bergamot „ Oil of origanum. 



Oil of origanum „ Oil of savory. 



Oil of savory „ Eixed oils. 



So also pure water repels many solutions of salts. A solution of alum 

 repels one of vitriol ; this repels sodic sulphate ; this potassic nitrate ; this 

 sodic chloride, and so on. 



25 Comptes Rendus for 1841, p. 690, which contains a Report on the 

 Memoir. 



