48 On the Motions of certain Liquids on the Surface of Water. 



explained by adhesion only, or by the resultant force of the ad- 

 hesion of the surface and the cohesion of the oil. For example, 

 a film of 01. Rutce sends out short processes from the edge, 

 which sometimes split at the free end and become bifurcated with 

 wide-spreading forks ; or the free end may terminate in a boss, 

 which is torn away and another formed. I have also observed 

 a hole to open in the centre of the film, showing colour ; after a 

 time the colour would disappear and streamers set in directed to- 

 wards the centre of the opening. Then the hole enlarged and 

 the film separated into two or three well-defined disks, which re- 

 mained quiet for a time, and at length put forth active streamers 

 from the edge, which sailed away and disappeared. The splitting 

 up and scattering over the surface on the part of some films I have 

 endeavoured to represent in the case of creosote in the plate 

 which accompanies one of my papers 25 ; and the spasmodic actions 

 which accompany separated portions of some other films are re- 

 presented in the subsidiary figures b, c, d which accompany the 

 engraving of the principal figure of oil of lavender 26 . The 

 waving to-and-fro motion of the film of oil of bitter almonds and 

 some other oils is very remarkable. In bright warm weather the 

 energy of some oils on a large surface of water is striking. A disk 

 of oil of cloves, for example, will set the whole surface vibrating 

 after the manner of camphor pulsations 27 . When one drop of 

 absolute alcohol was added to twenty drops of oil of cloves, and 

 one drop of the solution placed on the surface of water, the disk 

 that was formed shot out volleys of small globules with immense 

 velocity, which covered the surface, and then all became quiet. 

 In attempting to estimate the value of the cohesion-figure test 

 by adding small proportions of the fixed oils to the more costly 

 essential oils, an endless variety of phenomena was obtained, 

 which, as it seemed to me, only required to be studied in order 

 to render this test valuable. I refer to them now as affording 

 good illustrations of variations in surface-tension ; but it might 

 be tedious if these examples were prolonged. 



33. In conclusion, I must express my satisfaction that the 

 vast number of phenomena described or alluded to in this and 

 my former paper have been erected into a tasteful and harmo- 

 nious structure by the Belgian physicist. I have contributed a 

 good many bricks to the building ; but it is a privilege to serve 

 science, even though it be in the humble capacity of hod-carrier 

 to a master bricklayer. 



Highgate, N., Dec. 13, 1869. 



« Phil. Mag. for June 1867, Plate IV. 



26 Phil. Mag. for October 1861, PL IV. 



27 Phil. Mag. for December 1869, § 26. 



