378 Mr. C. Tomlinson on the Motions of Camphor 



"superficial attraction" (attrazione di superficie), which Dutro- 

 chet afterwards developed into the "epipolic force" {force epi- 

 polique). 



7. In 1819 Barlocci 9 covered fragments of camphor with gold 

 leaf, and found that they did not move on the surface of water. 

 The idea was that by preventing the formation of vapour, Ven- 

 turis theory, which attributed the motions to the escape of 

 vapour, would be supported. It is further stated that perfect 

 cubes of camphor do not move on the surface of water, on account 

 of their perfect symmetry. This, however, is a mistake which 

 several observers have fallen into ; and we suspect that the cutting 

 and shaping and handling of the camphor so as to confer upon 

 it a geometrical form made it dirty, and that this was really the 

 cause of its want of motion, I have frequently placed beauti- 

 fully formed oblate spheroids of camphor on the surface of water ; 

 and these have continued to move about during some hours : but 

 these figures were absolutely clean ; for they were formed by dis- 

 solving camphor in strong sulphuric acid, and depositing a drop 

 of the solution from the end of a clean glass rod upon the sur- 

 face of clean water in a catharized glass 3| inches in diameter. 

 The acid dialyzes off and leaves the camphor in a compact well- 

 shaped button. Two or three drops may be deposited on the 

 same surface ; and the resulting buttons will sport about for a 

 long time without interfering with each other's motions. 



8. In 1824 a writer in Thomson's 'Annals' 10 attributes the 

 motions of camphor on water to the fact that the centre of gra- 

 vity of each fragment and the centre of support are not in the 

 same vertical. Another anonymous writer 11 rejects this idea, on 

 the ground that, if true, every irregular floating body ought to 

 present the same phenomena as camphor. 



9. I may here remark that during the many years in which 

 the motions of camphor puzzled even the best observers, the idea 

 was not seldom started that the shifting of the centre of gravity 

 had something to do with the phenomenon. In 1863 Mr. 

 Trachsel 12 quotes an experiment by M. Gingembre (without 

 reference), in which a cylinder of camphor, ballasted at one end 

 with lead, was placed in water reaching halfway up the little 

 pillar. After twelve hours' contact the camphor was cut half 

 through at the level of the water, but not equally all round. 

 This experiment (which really originated with Venturi 13 ) is 

 quoted to show " the unequal power of solution in certain direc- 

 tions of the crystalline mass," and " this being one of the pro- 



9 Giorn. Accad. di Sci. Roma, vol. ii. p. 226. 



10 Second Series, vol. viii. p. 75. u Ibid. 



12 Chemical News, August 22, 1863. 



13 Annates de Chimie, tome xxi. p. 262. 



