The Motility of the Positive Ion in Flames. 775 



Ladenberg's correction for the effect of the walls of the 

 fall tube is independent of the viscosity, and holds for 

 spheres of radii not greater than one-tenth the radius of the 

 tube. 



Stokes's law, with the above correction, holds in the less 

 viscous liquids to within at least one-half of one per cent. 



The inertia terms begin to have an appreciable effect 

 when the radius of the sphere is about six-tenths of the 

 critical radius. 



The coefficient of sliding friction at the surface of the 

 solid spheres used is certainly greater than 5000, and pro- 

 bably greater than. 50,000. 



The theoretically derived formula involving the coefficient 

 of sliding friction holds in the case of complete surface slip. 



The slip at the surface of a bubble of gas rising through 

 a liquid may be either approximately zero or infinite. This 

 can be explained from the film-forming properties of the 

 liquids, and hence we may explain the irregularities of previous 

 experiments on the rise of air bubbles. 



A consideration of the erosion at the surface of an air 

 bubble leads to the possibility of a new method of deter- 

 mining the relative spheres of molecular attraction in 

 liquids. 



In Conclusion the author wishes to express his thanks to 

 Professor Michelson and the staff of the Ryerson Laboratory, 

 and especially to Professor Millikan, at whose suggestion 

 and with whose direct and inspiring supervision this work 

 was carried out. . 



LXXV. The Mobility of the Positive Ion in Flames. By 

 S. G. Lusby, M.A. (Sydney), Emmanuel College, Cam- 

 bridge, Barker Graduate /Scholar of the University of 

 Sydney *. 



(1) Introduction. 



THE determination of the mobilities of the ions produced 

 when certain salt vapours are introduced into a Bunsen 

 flame has occupied the attention of many experimenters since 

 Arrhenius f first set this type of work on an exact basis. 

 Most observers, however, have confined their attention to the 

 negative ion, owing to the rapid growth of our knowledge of 

 the negative electron. It has now been demonstrated beyond 



* Communicated by Sir J. J. Thomson. 

 t Arrhenius, Wied. Ann. 1891. 



