46 Mr. W. B. Hardy and Lieut. J. K. Hardy 



The basis of the original observation on the tea-cup is 

 revealed by these results. The sticking of the cup is not 

 due to the fact that a thick layer of homogeneous fluid 

 lubricates less than a thin layer, but to the fact that an 

 inactive fluid, in this case water, diminishes the effect of an 

 active fluid. There is much of scientific interest in the way 

 the water acts. It does not remove or even temporarily 

 detach the film of lubricant, for the full influence of the 

 latter is restored when the water is dried off. On the other 

 hand, it would seem to lessen the grip of the film on the 

 glass, for the latter can be detached by lightly rubbing the 

 surface under tJie water. 



G-biss 2. Paraffin. Film polished with linen : Threshold 

 value 10' 5 grammes. 17° 0. 



Flooded with water 18 grammes. 



Rubbed lightly under water with the 

 finger-tip, which had been freed from 

 grease by washing 36 ,, 



Rubbed more vigorously 41 ,, 



Glass 3. Castor Oil. Polished film : Threshold 

 value 11 grammes. 19° C. 



Flooded with water Pull 18 grammes. 



Rubbed under water with cleaned 



finger-tips ,, 43 ,, 



That the water should act by reducing the tenacity of the 

 film is quite in accord with the classical theory of capillarity. 

 When the film is formed of a solid, flooding the surfaces 

 with water has no effVct, the solidity of the film apparently 

 enabling it to resist the tangential stress. A solid film was 

 formed by coating a clean surface of glass with melted solid 

 paraffin. The excess was then polished off with linen until 

 nothing visible remained. The threshold value was found to 

 be 0*1 gramme per gramme weight. Flooding the surface 

 with water did not alter this value. 



Attention has already been drawn to the fact that ordinary 

 "pure "ether and benzene contain a lubricant in solution 

 and leave behind a lubricating film on evaporation. Rectified 

 spirit also contains an impurity which causes it to behave 



