on the Surface of Water. 531 



tive durations establish differences capable of numerical expres- 

 sion. Thus, while a drop of carbolic acid on the surface of 2 

 ounces of water has a very vigorous action which lasts less than 

 one minute (during which the disk diminishes in size until it 

 has disappeared), a drop of creosote has a less vigorous existence 

 which lasts five minutes, a drop of eugenic acid ten minutes, 

 and a drop of oil of cloves or of pepper still longer. In all these 

 cases a second drop placed on the water which received the first, 

 has a longer and less energetic existence, because the adhesion 

 of the water is partly satisfied. The duration of the first drop 

 also varies with the state of the weather, and the age and ex- 

 posure of the specimen. 



Dr. Gladstone was so kind as to furnish me with a specimen 

 of eugenic acid (G 10 H 12 O 2 ), and I cannot help thinking that 

 some of the results obtained with it are worthy of notice. 



A drop of this acid was placed on the surface of 2 fluid ounces 

 of distilled water contained in a glass capsule 2^ inches in dia- 

 meter. It formed a good lively figure, but quickly split up into 

 three disks, which in the course of two minutes ceased to vibrate. 

 They soon recovered their vigour and began sailing about and 

 revolving round each other; as they became smaller they in- 

 creased in vigour, and at length disappeared in wild gyrations. 

 A second drop placed on the same surface formed a disk which 

 immediately split into two portions ; these were active for the 

 moment, and then became quite still. After some minutes they 

 became active, not after the fashion of the first drop in sailing 

 about, but in slowly rotating on a vertical axis, as was evident by 

 watching one or two (resinified?) projecting points that had ap- 

 parently grown out of the edge of the disk. Each of these 

 points became the centre of a series of attractions and repulsions 

 of the delicate silvery scales that had been left on the surface by 

 the first drop. The scales apparently sailed up in regular lines 

 to each point, where they divided and turned aside right and 

 left*. On dusting a little lycopodium powder over the surface of 

 the water, the particles immediately formed currents about the 

 eugenic-acid disk, they being apparently attracted by the pro- 



* The figure produced is very much like that given in my paper " On 

 the Electrical Fly" (Phil. Mag. vol. xxvii. PL Il/fig. 6), where metallic par- 

 ticles in turpentine are attracted and repelled by the wires connected with 

 the machine and the earth. There is no reason to suppose that the eugenic- 

 acid attractions and repulsions are electrical in their origin, although 

 electricity may be a secondary result. I tried the experiment, in a metal 

 dish, on the plate of a gold-leaf electrometer, and found that when the 

 leaves are diverged either -4- or — , there is a trembling motion accompa- 

 nying the action of the eugenic-acid disk or of creosote &c. An erking 

 motion of the leaves is also produced when a film of oil spreads out on the 

 surface of the water. But my apparatus is not sufficiently delicate for such 

 experiments. 



2M2 



