422 Mr. C. Tomlinson on the Motions of Camphor 



sition : — When on the surface of a liquid, A, we deposit a small 

 fragment of a solid, B, which is more or less soluble in A, or 

 detaches from its surface matter that is so, the equilibrium of 

 the superficial layer of A is disturbed. If the solution take place 

 equally all round the fragment, this does not move ; if unequally 

 in different azimuths, the fragment displays sudden movements 

 of translation and rotation. 



35. In order to show the action of camphor in diminishing 

 the surface-tension of water, flexible filaments were taken, 30 or 

 40 centims. in length. On scraping a few fragments of camphor 

 upon the space defined by the filaments, these were quickly 

 thrown into the form of a perfect circle. The camphor produced 

 great diminution in the contractile force of the water, reducing 

 it to 4*5 ; and as this diminution takes place unequally round 

 each fragment, this must necessarily rotate. If the camphor be 

 placed outside the ring, the filaments immediately contract. 



36. By repeatedly adding fragments of camphor to the water, 

 this became reduced in tension to 4*5, and the camphor no 

 longer rotated. Or if the surface be touched with the finger, 

 the tension is reduced to 4*75 in consequence of a greasy film 

 being transferred to the water. A similar effect is produced by 

 an unclean vessel, or the presence of smoke, or of the vapours of 

 essential oils &c. in the air of the room. 



37. The various bodies that rotate on water act like camphor 

 in locally diminishing its surface-tension. The reason why the 

 motions are not in general observed on the surface of oils, spirit, 

 &c. is, that their surface-tension is feeble, although their adhe- 

 sion to the camphor &c. is sufficiently energetic to dissolve it. 



38. There are many circumstances which render this theory more 

 acceptable than the recoil theory, which has so long found favour in 

 accounting for these motions. For example, in one of the experi- 

 ments described in my essay (note 3 ), a well-shaped lens of water 

 with a well-defined rounded edge was formed on a glass plate, and 

 also on the surface of clean, pure mercury, and on this lens mi- 

 nute fragments of camphor were set spinning. I observed that 

 the fragments would often pass over the edge and rotate in a nearly 

 vertical taugent plane, and then go back again to the upper sur- 

 face of the lens. A similar effect was also noticed with phos- 

 phorus on the surface of mercury. I could not understand by 

 what influence the fragments recovered their position from a 

 nearly vertical to a horizontal plane. The surface-tension theory 

 makes it clear. Another difficulty was that the rotations of bits 

 of paper smeared with oil are very rapid on the surface of water, 

 notwithstanding the friction ; flakes of camphor, formed by ex- 

 posing oil of camphor to the air, or flakes of benzoic acid, formed 

 by a similar exposure of oil of bitter almonds, move with even 



