38 Mr. C. Tomlinson on the Motions of certain 



the ether-vapour has scarcely any action on its surface ; while 

 there is no action at all with a solution of one part of saponine 

 in sixty parts of water, although # = 4*67, the viscosity of the 

 surface of this solution being very great. On such a surface a 

 drop of turpentine spreads almost as slowly as upon a solid 

 surface. 



14. A, carbonic disulphide (a = 35 7); B, alcohol ; = 0*30. 



In this case the observation is difficult, because the particles 

 floating on A are being constantly displaced by spontaneous 

 movements, arising from variations in tension at different parts 

 of the surface consequent on the evaporation of A (clogged as it 

 is by the powder dusted on) being unequal. This produces a 

 lowering of the temperature, the effect of which is to increase the 

 superficial tension of a liquid in proportion as such reduction is 

 great. It was evident, however, that the alcohol-tube did act 

 in producing the apparent repulsion of the powder. 



15. A, absolute alcohol ; B, carbonic disulphide; = —0*30. 



Since the difference in the tensions of the two liquids is negative, 

 the motion on the part of A subjected to the vapour of B is no 

 longer centrifugal, but centripetal. The alcohol was in a cap- 

 sule of from 20 to 25 centims. diameter, and on the surface 

 were dusted some light particles of bran ; then holding very near 

 the surface a tube of not more than 1 millim. diameter contain- 

 ing a small drop of the disulphide, particles at the distance of 

 from 4 to 5 millims. floated up and remained stationary under the 

 tube. In fact the vapour of the disulphide condensing on the 

 surface of the alcohol augments somewhat its tension, and thus 

 produces an attractive effect on the neighbouring particles. 



16. If in this experiment a tube of 3 or 4 millims. be used, 

 the particles are first attracted near to the drop and then imme- 

 diately repelled. The author explains this by supposing that the 

 condensation of the vapour slightly augments the temperature 

 of the subjacent portion, while evaporation is diminished there 

 by the presence of the tube and of the disulphide vapour. 

 But the surrounding portions of the alcoholic surface evaporate 

 freely, and so acquire an exaltation of tension more than suffi- 

 cient to counterbalance the increased tension of that part of the 

 surface just below the tube. In fact it can be shown that if 

 evaporation be interrupted at one part of the surface of the 

 alcohol, the neighbouring parts pull upon it, as is evident from 

 the apparent repulsion of the particles on the surface. 



17. A, carbonic disulphide ; B, oil of turpentine; =0*19. 





