a Chemically Clean Surface. 245 



space of about two inches in diameter is formed as by a flash, 

 arising from the production of a film of camphor, which, being 

 instantly disposed of by solution and evaporation, makes way 

 for another film, which disappears in like manner; and by this 

 very process the surface is kept clean for further action. The 

 solution travels on in lines corresponding with the faces of the 

 stick of camphor, and as the lines reach the side of the glass 

 they divide right and left, and are reflected inwards in curves, 

 the effect of which is to form the lycopodium into pairs of re- 

 volving wheels, the two members of each pair revolving in op- 

 posite directions. I have had this effect in active operation 

 during fifty hours, merely taking the precaution to lower the 

 camphor as it became cut through at the surface of the water. 



Another remarkable continuous action is maintained by cam- 

 phor in what I have named " camphor pulsations "*. If a stick 

 of camphor be lowered into shallow water, contained in a flat 

 glass dish 6 or 7 inches in diameter, so that the camphor may 

 touch the bottom of the vessel, the water will be thrown into 

 rapid pulsations. On a fine bright day I have counted as many 

 as 240 per minute; but the number rapidly declines to about 

 80, and the pulsations may continue at that number during some 

 hours. So regular is the beating, that on one occasion a medical 

 friend who came in while the experiment was going on instinc- 

 tively took out his watch and counted the beats, which he said 

 were exactly like those of the pulse. The effect is, indeed, merely 

 a case of capillarity : the water rises some Avay up the camphor 

 and detaches a film, which spreads by the adhesion of the water- 

 surface ; while spreading, the water sinks about the camphor- 

 stick ; but as soon as the film is disposed of by solution and eva- 

 poration the water rises again, detaches another film, which is 

 disposed of as before ; and thus the surface is kept clean for con- 

 tinuing the action. As the water becomes more and more im- 

 pregnated with the camphor, the action slackens; and as succes- 

 sive films are detached all round the camphor-stick both above 

 and below the level of the water, the action becomes more and 

 more striking. 



Of course in all these experiments, if the finger or other che- 

 mically unclean body be made to touch the water, the actions are 

 brought to an end. 



But it has been said, during the last century and longer, that 

 if, while the camphor is rotating, the surface of the water be 

 touched with an oil or anything oily or greasy, the camphor 

 motions are instantly and permanently arrested. This statement 

 requires considerable limitations. 1 have already shown f that 



* Chemical News for 1863, vol. viii. p. 37. 

 t Phil. Mag. for September 1863. 



