532 Mr. C. Tomlinson on the Motions of Eugenic Acid 



jecting points of the disk and repelled at the smooth parts. (See 

 Plate VI. figs. 1 and 2). As the disk became smaller, it got en- 

 tangled with some particles of the powder, and spun round with 

 great velocity, very nearly like a small fragment of camphor on 

 water. The larger disk also broke up and the separate portions 

 moved over the surface with vigour. The lycopodium was power- 

 fully driven away in front of the advancing disk, while other por- 

 tions were dragged into its wake. It had occasional intervals of 

 of repose, during which the currents set in in regular order. The 

 experiment had now lasted two hours, and still these alternations 

 of activity and repose were maintained. The various disks in 

 their wanderings always avoided each other, and in throwing off 

 separate portions, these formed independent disks, while the 

 parent disk thus lightened would go wandering about as if in 

 search of something, and then, as if it had found a fixed axis, 

 would whirl round with great rapidity, at the same time throwing 

 off small fragments which, of course, whirled still more quickly. 

 At length, as if weary of this rapid work, the disks became quiet, 

 and remained so for many minutes. It often seemed as if a loud 

 sound, a railway whistle, or a noise in the room, set the disks 

 spinning again. 



This second drop lasted 2\ hours. A third drop produced a 

 powerful repulsion of the lycopodium particles, as in the case of 

 camphor, and in like manner there was a pause, and then a setting 

 in of currents with apparent attractions and repulsions. The disk 

 soon began to spin on a vertical axis, and then to make wide 

 sweeps over the surface. After five hours the disk was still 

 moving slowly about, but the next morning it was quite motion- 

 less. The water was run through a filter, and returned to the 

 capsule. Another drop of eugenic acid (the fourth) was placed 

 on the surface, and fresh lycopodium powder was dusted on ; 

 there w T as a very feeble action. The water was evidently satu- 

 rated ; and to prove that the motions described are mainly due 

 to solution, a small quantity of water was added to the saturated 

 solution, when the disk split up, the lycopodium currents set in 

 with vigour, and the smaller disks went whirling about as before. 

 After some hours, saturation was again attained, and a fresh 

 drop of eugenic acid was perfectly passive. 



To try the effect of an enlarged surface, the same quantity of 

 water (2 oz.) was poured into a shallow vessel 4 inches in 

 diameter (the capsule being only 2^ inches). A drop of eugenic 

 acid on this surface split up into numerous active disks, which 

 disappeared in 11 minutes, while in the capsule the duration 

 was 30 minutes. A second drop produced a much less active 

 disk ; it sailed slowly about for an hour, then suddenly became 

 remarkably vigorous, and disappeared in another 15 minutes. 



