188 Mr. (J. Tomlinson on the Action of Oils in 



the camphor-motions only during its solution and evaporation, 

 and that when got rid of by those processes the motions will set 

 in as before. This remark was not meant to apply to all the 

 essential oils ; and some results that I have lately obtained define 

 the conditions of the limitation. 



A flat glass dish, 6 inches in diameter, made chemically clean, 

 was nearly filled with clean water, and some fragments of cam- 

 phor from a freshly- cut surface were scraped upon the water with 

 the point of a penknife- blade. The fragments rotated with great 

 vigour. A drop of " rectified spirits of turpentine " was gently 

 delivered to the surface of the water from the end of a glass rod; 

 the turpentine flashed out into a film, and the camphor frag- 

 ments were struck motionless — comme foudroyees, as Prevost 

 has it, or "as if by magic/'' according to Venturis remark. 

 Fresh fragments of camphor were thrown on the surface at in- 

 tervals during thirty hours, but no motion was produced. 



Camphor was set spinning in a similar clean vessel, and a drop 

 of oil of rosemary was placed on the surface ; the film instantly 

 arrested the motions, but in about forty minutes fresh fragments 

 rotated briskly. 



The experiment was repeated several times with different oils, 

 &c, with similar results : the oils were cajeput, patchouli, car- 

 raway, cubebs, eucalyptus, and some others, as also creosote and 

 carbolic acid. This additional fact was noticed with respect to 

 the oily films of carraway and cubebs — that fresh camphor frag- 

 ments rotated briskly in them. It was also found that a drop 

 of the oil of bitter almonds or of aniseed does not arrest the 

 motions of the camphor fragments at all. 



I may here remark that oil of aniseed is well adapted to ex- 

 plain what seems to me to be the true cause of the camphor- 

 motions, namely that a film is detached from the camphor itself 

 by the adhesion of the water, which film, reacting on the frag- 

 ment, produces motion after the manner of the electrical star, 

 Barker's mill, &c. The oil of aniseed becomes solid so readily 

 at a moderate degree of cold, that fragments of it may be used 

 to show rotations on water after the manner of camphor. In the 

 case of camphor, the motions are very rapid, and the film that 

 produces them is, under ordinary circumstances, invisible ; 

 whereas in the case of solid aniseed these rotations are slow and 

 the film visible, so that the action can be studied under the great 

 advantage of having all the conditions at command. The film 

 from the fragment of aniseed is pushed forward in one direction, 

 while the fragment itself moves in the opposite direction ; and 

 this continues until the adhesion of the surface is satisfied, and 

 then the motions are brought to an end. If the film, as fast as 

 it is formed, is got rid of by solution and evaporation, as in the 



