40 Mr. C. Tomlinson on the Motions of certain 



19. Effects of this kind I endeavoured to explain by supposing 

 the liquids, in passing into vapour, were endowed with a repul- 

 sive force; but when such vapours condensed on the film and 

 became soluble in it, attraction set in accompanied by an increase 

 of cohesion. I fully admit the great superiority of the theory 

 which accounts for and explains these varied effects by variations 

 in the surface-tension. Some of the phenomena just given (18), and 

 others to which I shall afterwards refer (28) (32), always puzzled 

 me until I saw what a vast number of analogous phenomena were 

 generalized by the theory of the surface-tension of liquids. 



20. There is one of my results which Professor Van der Mens- 

 brugghe explains in a manner that does not seem to me alto- 

 gether to meet the phenomena. I state two effects : (1) that 

 the oil-of-turpentine sponge produces beautiful iridescent rings 

 when held over a film of oil of turpentine ; (2) that when the 

 film or cohesion-figure has passed into what I call its fourth 

 phase 13 , and a lace-like pattern is left on the surface of the water, 

 if a drop of oil of turpentine be held over the surface the parts 

 will gather together and display colours. On referring to my 

 note-book, I find the first effect also entered for the oils of rose- 

 mary and mint, and also for balsam of Tolu ; that is, a film of 

 one of these would display iridescent rings by the action of 

 its own vapour. These experiments were first made in bright 

 summer weather, which is so favourable to all the camphor and 

 other surface-motions. On attempting to repeat them recently 

 I failed ; that is, I got no repulsion or thinning of the film by 

 the action of its own vapour upon it. When the film had become 

 attenuated by evaporation, I obtained the iridescent effects by 

 the action of the turpentine-sponge. This arises, according to 

 the theory, from an increase in thickness consequent on the con- 

 densation of vapour; and as the tension of the water so covered 

 diminishes up to a certain limit in proportion as the thickness 

 of the film is increased, it will be understood how, as the tension 

 becomes less in the coloured portion, the surrounding parts 

 remove this from the centre until the white of the first order is 

 again developed at this centre. The rings then remain station- 

 ary, or even become slightly compacted by virtue of the tension 

 of the central part. The condensation of a fresh portion of va- 

 pour only slightly changes the aspect and diameter of the rings, 

 so that the central white remains. When the source of vapour 

 is removed, the rings disappear and the white tint covers the 

 whole film. 



13 The drop of turpentine on water forms (1) a well-defined film, with a 

 double row of bosses of unequal size just within the edge ; (2) the film dis- 

 plays iridescent colours; (3) it becomes perforated with small holes ; (4) it 

 forms a delicate network. 



