536 On the Motions of Eugenic Acid on the Surface of Water, 



on the surface of water*. On the surface of acetic acid a drop of 

 oil of cloves is far more energetic than on water, on account of 

 its greater solubility in that liquid. It forms a very beautiful 

 figure, reminding one of the sun in a fog, darting out rays and 

 surrounded by a halo. The experiment was performed in a 

 watch-glass. Feeble currents may also be noticed when a drop 

 of paraffin oil is placed on the surface of pyroligenous ether. 



The motions that have now been described seem to be due to 

 the contest that takes place between the adhesion of the water 

 and the cohesion of the drop in a substance of small solubility 

 and volatilit3 r . As in the case of camphor, creosote, and a few 

 other substances, the contact of water detaches from the eugenic 

 acid an invisible film which surrounds the disk and exerts a 

 repellent action all round. This film immediately enters into 

 solution, and gives place to other films, which are similarly 

 disposed of. This annular film, constantly given off by the 

 eugenic-acid disk, prevents oils from touching it, and produces 

 repulsion in the lycopodium powder. The first drop of acid is 

 thus got rid of, and the adhesion of the water is so far impaired 

 that, soon after the second drop is placed on the surface, the 

 disk forms around it not an annular film, but portions only 

 of a film, which spread out from the disk in broad lines or 

 channels {a, b, c, fig. 3) . Besides this, the second drop is exposed 

 to the air so much longer than the first that partial resinification 

 sets in at two or more points in the circumference of the disk. 

 We have now the conditions favourable for the apparent attraction 

 and repulsion of the particles. For if E (fig. 3) be the eugenic- 

 acid disc, a } b, c the portions of film given off by it preparatory 

 to entering into solution, and r r resinified points in the circum- 

 ference of the disk, the radial portions, a, b y c } being constantly 

 given off will repel the particles of lycopodium powder and drive 

 them into the tranquil space t, where they will be constrained by 

 other particles behind them to move forward towards the point r, 

 but at and about this point they will be dragged into the currents 

 formed by ss, and be again carried forwards or repelled in the 

 direction of the arrows. 



I have spoken of resinified points in the edge of the disk as 

 being necessary to the formation of the circulating currents. If 

 resinified, the points are inert ; and any other inert substance 

 ought to produce the same effect. A few specks of lycopodium 

 powder at the edge answer very well. Thus in fig. 2, where the 

 black specks represent particles of powder, currents are established 

 as before, the flow of the particles towards the oil-disk not being 

 the result of any attraction, but simply of a repulsion of the sur- 



* The oil of pepper used by me was obtained from the Jamaica Court 

 of the International Exhibition. 



