490 Royal Society. 



" On the Absorption and Radiation of Heat by Gaseous Matter." — 

 Second Memoir. By John Tyndall, Esq., F.R.S. (See Phil. Mag. 

 for October.) 



February G*. — Major-General Sabine, R.A., President, in the Chair. 



" On the Motions of Camphor on the Surface of Water." By 

 Charles Tomlinson, Esq. 



The object of this paper is to show that the phenomenon in ques- 

 tion is a much more general one than is commonly supposed ; that 

 the explanations hitherto given of it have been insufficient or erro- 

 neous. The author endeavours to explain the real nature of the 

 phenomenon in a series of experiments and observations, and to esta- 

 blish the following propositions : — 



I. That the camphors, or stearoptens of the volatile oils, present 

 phenomena of rotation and progression when thrown on the surface of 

 clean water in a chemically clean vessel. 



II. That these phenomena belong also to certain salts, and to a 

 variety of vegetable and other substances containing a liquid that 

 diffuses readily over the surface of water. 



III. That solutions of camphor in benzole, in some of the essential 

 oils, &c, present phenomena of rotation and progression on the sur- 

 face of water — a property which also belongs to creosote, and to some 

 other liquids that do not contain camphor. 



IV. That the motions of camphor may be imitated by placing on 

 water miniature rafts or coracles of inert substances, such as talc, 

 tinfoil, paper, &c, smeared with or containing the elaeoptens of vola- 

 tile oils, or indeed any volatile liquid, such as ether, alcohol, chloro- 

 form, &c, provided there be some communication and adhesion be- 

 tween such liquid and the surface of the water. 



V. That the camphors, &c, being slightly soluble in water, that is, 

 the adhesion of the water partly overcoming the cohesion of the cam- 

 phor, a film of camphor is thus detached from it, and spread over 

 the surface of the water the moment that the camphor comes in 

 contact therewith. 



VI. That the dimensions and form of this film depend on those 

 of the piece of camphor operated on ; and, in general, the film sepa- 

 rates more easily from broken surfaces and angles of the fragment 

 than from a smooth natural surface, just as the crushed or broken 

 surface of a crystal is more soluble than a perfect crystal. 



VII. That such films being constantly detached from the cam- 

 phor so long as it is in contact with the water, displace each other ; 

 the preceding film being conveyed away by the adhesion of the 

 water in radial lines, these produce motion, by reaction on the frag- 

 ment, causing it to rotate after the manner of a Barker's mill. 



VIII. That these radial lines or jets being of unequal intensity, the 

 direction and intensity of the motion will follow that of their resultant. 



IX. That the jets or films of camphor can be rendered sensible 

 by various means — as by fixing the camphor partly submerged in 

 water, and dusting the surface lightly with lycopodium powder : a 

 series of horizontal currents produced by the films will then be 

 made visible, which films or jets cause the camphor, when free 

 to move, to rotate on a vertical axis. 



