the Motion of Spheres through Liquids. 



i iO 



Among the liquids used aniline approaches most closely 

 to linseed oil in its film-forming properties. It will be re- 

 membered that it was with aniline that Allen obtained such 



irregular results. 



Fiff. 10 shows the results o£ observations 

 Fiff. 10. 



7 8 9 10 II 12 13 14 

 DtsTqwcc .Traversed in Meters 



on an air babble in this liquid. Both curves are irregular, 

 but as a rule the low points of "the velocity curve correspond 

 to points on the v l curves where the radius is diminishing 

 most slowly. These results are easily explained on the as- 

 sumption that a film forms with a great readiness in this 

 liquid, but is also easily destroyed. The slow velocities and 

 slight decrease in size correspond, then, to the existence of a 

 film ; the high velocities and faster decrease to the absence 

 of a film. This explains how Allen could obtain some velo- 

 cities so much larger than those computed on the assumption 

 of no slip, and yet obtain others so nearly in agreement with 

 the computed values. 



Of the oils used, linseed oil and glycerine showed lpast 

 evidence of surface slip ; castor oil, colza oil, machine oil, 

 cottonseed oil, and paraffin oil agreeing more nearly with 

 olive oil in their behaviour. Since, however, the amount of 

 slip is a function not only of the kind of oil but also of the 

 size of the bubble, it would be meaningless to speak of the 

 coefficient of slip of a particular oil. Our picture of the sur- 

 face conditions which give rise to the appearance of slip 

 would, indeed, lead us to predict that the slip at the surface of 

 a sufficiently large bubble would appear infinite in any liquid. 



