416 Mr. C. Tomlinson on the Motions of Camphor 



the morsel of camphor, and probably also by its immediate 

 contact" 28 . 



24. In 1861-62 I was led by the phenomena of cohesion- 

 figures to pay some attention to the motions of camphor &c. on 

 water 29 . It was evident that Carradorr's attraction of surface 

 exerted a powerful influence on the phenomena, since a globule 

 of creosote, carbolic acid, &c. on the surface would sail about and 

 exhibit the most lively motions and even be torn to pieces and 

 disappear in the course of some seconds, while below the surface a 

 drop would remain as a globule unchanged for hours or even days. 

 So also a drop of a solution of camphor in benzole &c. would move 

 over the surface, darting out waving tongues and so disappearing. 

 But phenomena of this kind seemed to be simple effects of ad- 

 hesion of surface, tending to overcome the cohesion of the drop 

 by spreading it out into the form of a film ; and the various 

 amounts of resistance offered by different liquids led to such dif- 

 ferent resultant phenomena as those of cohesion-figures, and the 

 various motions of camphor and other bodies. But in the case 

 of camphor and other solid bodies, not only was a film detached 

 from its surface by the adhesion of the water, but the reaction 

 of this film on the fragment seemed to be a sufficient force to 

 account for its gyrations. It is true that in the case of camphor 

 the film is not visible, but in many other cases this objection 

 does not apply. Oil of aniseed, for example, solidified by cold, 

 gyrates like camphor, only more slowly, with the advantage of 

 leaving a filmy trail on the surface. A fragment of this oil on 

 water, apparently performing the whole of its work under the 

 eye of the observer, seemed to give irresistible proof of the truth 

 of the theory, viz. that the adhesion of the water detaches a film 

 from the solid, which film in the act of spreading on the surface, 

 produces motion by reaction. If the film remain on the surface 

 the motion ceases ; but if it be rapidly disposed of by evaporation 

 and solution, the motion may continue so long as the fragment 

 lasts. If proper arrangements be made, motions which admi- 

 rably represent the phenomena may be kept up for days together. 

 For example, if a three- or four-sided stick of camphor held in 

 forceps be made to dip just below the surface of clean water pre- 

 viously dusted with a very thin coating of lycopodium-powder, a 

 film is detached from each side of the camphor the moment it 

 touches the water; there is instant repulsion of the powder as 

 by a flash ; then a momentary pause, during which the film is 

 disposed of by evaporation and solution ; another film is detached 

 in like manner, and the solution of camphor from each film, cor- 

 responding with each side of the stick, travelling on, or rather 



28 Recherclies Physiques sur la Force Epipolique, part ii. p. 160. 



29 See note 3 . 



