196 Prof. H. A. Wilson on the Application of 



dense lasting froth, may involve, in the value of the surface 

 tension, a diminution, under isothermal conditions, of only 

 about one per cent. The suggestion is made that the dis- 

 ruption of the surface, which results in the small bubbles, is 

 due to a high gas pressure associated with a weakening of 

 the surface tension in small patches, which may occur in a 

 newly formed surface while the surface concentration is 

 acquiring its full value, or in the case of an oil-contaminated 

 liquid, may be caused by the appearance of small oil spots on 

 the surfaces of large bubbles, resulting from the contact of 

 the bubbles with minute drops of oil disseminated, by the 

 a citation, throughout the liquid. 



XIV. Note on the Application of Thermodynamics to the 

 Discharge of Electricity by Hot Bodies. By Prof. H. A. 

 Wilson, F.R.S., McGill University, Montreal*. 



IN 1903 the writer published a calculation of the current 

 carried by the ions emitted by a hot body as a function 

 of the temperature based on thermodynamical reasoning f. 

 The result obtained may be expressed in the following form : 



^ = A 0(l+«/K) e -^ o /R0 ? . . . . , (1) 



where p is the equilibrium pressure due to the ions emitted 

 at absolute temperature 0, R the gas constant, A a constant, 

 and iv the work required for an ion to escape is supposed 

 given by the expression 



w = w + a6 



where a is a constant. According to this the form of the 

 function p depends on the value of the constant a. 



In a recent number of the Philosophical Magazine Prof. 

 0. W. Richardson J has given a similar calculation of p 

 as a function of 0, but has come to the conclusion that the 

 form of the function is unaltered when w instead of being- 

 constant is a linear function of the temperature. 



The difference between the two conclusions is due to the 

 fact that Prof. Richardson has neglected a term in his 

 equations which is only negligible when the constant a has a 

 particular value. 



* Communicated bv the Author. 



f Phil. Trans. A. vol. ccii. pp. 243-275. 



| Phil. Mag. April 1912. 



