on the Surface of Water. 529 



surface of water seem to depend (1) on the formation of a film 

 of camphor which is detached from the fragment by the adhe- 

 sion of the water ; (2) on the reaction of such film on the frag- 

 ment ; (3) on the evaporation, and (4) on the solution of the film. 

 In this way a film is always being produced and always being 

 disposed of; but this incessant formation of the film which pro- 

 duces the recoil of the fragment, and also the evaporation of the 

 film, are limited to the surface, while the whole body of the 

 liquid is concerned in its solution. The motions of the frag- 

 ment are retarded or arrested (1) by impurity, especially a 

 slight greasiness on the water, whereby adhesion between the 

 surface of the water and the camphor is prevented ; (2) by the 

 presence of damp air, or by covering up the vessel, whereby the 

 evaporation of the film is prevented ; (3) by saturation of the 

 water, whereby the formation of the film is prevented. 



This liberation and spreading of the camphor-films over the 

 surface of the water, may be shown in a striking manner by 

 causing a stick of camphor to dip into water over which lyco- 

 podium powder has been lightly dusted. The moment the 

 camphor touches the water there is a wide repulsion of the 

 powder, and presently a series of currents set in from the centre 

 to the circumference, throwing the powder into the form of 

 pairs of wheels, the members of each pair revolving in opposite 

 directions. This action may in dry warm weather be kept up 

 for days together*. 



If the stick of camphor be brought down into a large shallow 

 vessel of water, such as a glass dish 5 or 6 inches in diameter, 

 the surface of the water will, by the liberation of these films, be 

 thrown into a state of vibration. At first as many as 250 pul- 

 sations may be counted in a minute, but as the water becomes 

 saturated, the number declines to 60 or 70. As the action con- 

 tinues, regular ripple-marks are cut into the camphor in deepen- 

 ing lines, at and about the level where the air and the water meetf. 

 Under favourable conditions the water will ascend and wear away 

 the camphor as much as -j^th of an inch above the common 

 level, and be depressed as much, the ascent and subsequent 

 descent forming one slow pulsation. 



The above experiments refer to common refined laurel camphor. 

 Crude camphor, from which it is prepared, rotates well on the 

 surface of water, as do also Borneo camphor, turpentine camphor, 

 camphoric acid, solution of camphor in sulphuric acid, in benzole, 

 chloroform, &c. Fragments of succinic, of benzoic, or of citric 



* These effects are fully described in a small volume entitled " Experi- 

 mental Essays " published in 1863. 



t The formation of this incision was first pointed out by Venturi in 

 1/99 {Ann. de Chimie, vol. xxi. p. 262). 



Phil. Mag. S. 4. No. 185. Suppl. Vol. 27. 2 M 



