on the Surface of Water. 415 



Academy of Sciences a memoir which clashes a good deal with 

 Dutrochet/s (21) ; and the noise is heard at intervals during this 

 and the first half of the following year. The authors do not 

 seem to have added much to the subject in hand. They found 

 that thin slices of cloves, pepper, orange-peel, &c. rotated on 

 water, and that naphthalin, though motionless on the surface of 

 water, rotated briskly on that of mercury. The advantage of 

 working with mercury is that it renders visible effects which are 

 not seen on the surface of water. 



23. Although Dutrochet's researches. (21) occupy nearly 

 seventy pages of the Comptes Rendus between the 4th of January 

 and the 5th of April, 1841, he felt that he had published them 

 with too much precipitation, and accordingly retired for awhile 

 in order to reconsider the whole subject. This led to the pub- 

 lication of a separate work, in two parts 26 , in which not only 

 the motions of camphor, but a vast number of other interesting 

 facts are traced to the influence of a force residing on the surface 

 of liquids, and hence named epipolic (iTuiroXri, surface). He does 

 not admit, and probably did not see, that this is nothing more 

 than another name for Carradori^s attraction of surface (9), (13), 

 (16), (17) ; for he does not seem to have been master of the 

 Italian language, in which Carradorr's earlier memoirs are printed, 

 and that at a time when the noise of conquest would scarcely 

 allow the voice of science to extend so far as from Italy to France, 

 unless it were unusually loud, as when Galvani and Volta spoke 

 for her. In the early part of his work Dutrochet says that " when 

 a bit of camphor is placed on the surface of water, there forms 

 around it a portion of camphorated water, which immediately 

 becomes endowed with a rapid centrifugal extension due to the 

 development of the epipolic force. The morsel of camphor, sur- 

 rounded by camphorated water incessantly renewed and inces- 

 santly projected circularly on the surface of the surrounding 

 Water by a kind of intermittent explosion, must necessarily par- 

 take by reaction of the motions of the liquid which surrounds it, 

 and receives from it those motions of progression which we see it 

 execute on the surface of the water. Such is, in short, the cause 

 of this phenomenon" 27 . In the second part of his treatise he 

 says : — (i The motion of camphor on water is an effect of reaction 

 produced by heat-repelling epipolic currents, which are formed 

 near the small fragment of this volatile substance, especially near 

 its points or angular parts" (part ii. p. 159). " Everything 

 concurs to prove that these epipolic currents, produced on water 

 by a morsel of camphor placed on the surface of that liquid, are 

 due to the local heat developed on such surface by the vapour of 

 26 Recherches Physiques sur la Force Epipolique, part i. 1842; part ii. 

 March 1843. 27 Ibid, part i. p. 74. 



