410 Mr. C. Tomlinson on the Motions of Camphor 



been published on the subject ; and it is chiefly from the account 

 then given 3 that the following details are condensed. 



4. In 1686 Dr. Heyde 4 noticed that when fragments of cam- 

 phor placed on olive-oil are viewed under the microscope certain 

 currents are observed, particles setting out, as it were, from a 

 centre and returning to the same point. 



5. In 1748 Romieu 5 first described the rapid, gyrations of 

 camphor on the surface of water : the motions are favoured by 

 heat, and their cause is referred to electricity. 



6. In 1773 Dr. Franklin 6 , in his account of the effects of oil 

 in stilling the waves, states that being about to show the expe- 

 riment to Smeaton the engineer, on a small pond near his house, 

 he was informed by Mr. Jessop, a pupil of Smeaton' s, that in 

 cleaning an oily cup in which some flies had been drowned, he 

 threw the flies upon water, when they began to spin round very 

 rapidly as if they were vigorously alive. " To show that this 

 was not any effect of life renewed by the flies," says Franklin, 

 ", I imitated it by little bits of oiled chips and paper cut in the 

 form of a comma of the size of a common fly, when the stream 

 of repelling particles issuing from the point made the comma 

 turn round the contrary way." 



7. In 1785 Lichtenberg 7 notices that the camphor experiment 

 succeeds best on warm water, or when the room is not very cold. 

 On plunging a thermometer into water at 130° the motions sud- 

 denly ceased, in consequence of some alteration in the surface ; 

 or, as he says, the thermometer may not have been quite clean, 

 so that the water became covered with a thin film. He refers 

 the motions of the camphor to the varying attractions consequent 

 on the constant change in form of the fragments brought about 

 by solution and evaporation. He disproves the electrical theory 

 of Romieu (5). 



8. In 1787 Volta 8 examined the experiment with great care. 

 He refers the motions to an effluvium which escapes from the 

 camphor explosively after the manner of a firework, and pro- 

 duces motion by the force of reaction. Similar motions are pro- 

 duced by benzoic acid, salt of amber (succinic acid), and volatile 

 concrete alkali (carbonate of ammonia). Salt of amber is parti- 

 cularly recommended, as it makes manifest to the eye the cause 

 of the motions ; for the fragment is evidently driven back from 



3 Experimental Essays, published in Weale's series, 1863. Essay I, On 

 the Motions of Camphor on Water. 



4 Centuria Observationum Medicarum. Amsterdam, 1686. Obs. LVI1. 



5 Hist, de VAcad. Roy. des Sciences de Paris, 1762. 



6 Letter to Dr. Brownrigg, November 7, 1773. Posthumous Writings 

 of Dr. 13. Franklin, F.R.S.&c. London, 181.9. Part IV. p. 268. ' 



7 Delectus Opusculorum Medicorum, edited by Frank. Ticini, 1787. 



8 Ibid. 



