﻿Charges on Thermions produced in Air and Hydrogen. 173 



to be a very sensitive indicator o£ thermal equilibrium. It 

 is questionable, indeed, whether it ever has been observed 

 hitherto. Finally, as regards conclusion (3), it seems to be 

 corroborated by Young's remark (p. 814) about a wider 

 limit or opalescence for positive than for negative deviations 

 from the critical temperature. 



It may be noted that a similar theory refers to the analogous 

 phenomena near the critical point of separation of binary 

 mixtures*. The opalescence of the two coexisting liquid 

 phases below this point does not seem to have been observed 

 hitherto, no doubt only owing to the difficulty of establishing 

 the equilibrium of concentration. 



Experimental work on these phenomena is of considerable 

 theoretical importance, since, according to the kinetic theory, 

 they are a direct evidence of a quality of matter out of 

 reach of ordinary thermodynamics : its intrinsic inhomo- 

 geneousness. Besides, the determination of the opalescent 

 curves ought to be the most exact method of determining 

 critical temperature and density, and generally of the shape 

 of the equation of state in the neighbourhood of the critical 

 point. 



XIV. The Charges on Thermions produced in Air and 

 Hydrogen at Atmospheric Pressure. By J. C. Pomeroy, 

 M.A., Fellow in Physics, Princeton University -\. 



IN view of the work done by 0. W. Richardson and F. C. 

 Brown % on the value of the specific charge and the 

 kinetic energy of positive and negative thermions it was 

 thought advisable to determine the value of the charge itself. 

 It was intended to make some preliminary tests in air at 

 atmospheric pressure, and in some other gases, and then try 

 the effect of reducing the pressure. However, some results 

 were obtained at atmospheric pressure which, while of no 

 special meaning in connexion with the experiments made at 

 low pressures already referred to, have still some little 

 interest in themselves. The method adopted was practically 

 that used by Townsend § in his work on the ions produced by 

 secondary Rontgen radiation. The essential part of the 



* Cf. Smolucliowski, Ann. d. Phys. xxv. p. 219 (1908) ; Einstein, 

 Ann. d. Phys. xxxiii. p. 1295 (11)1 1). 



t Communicated lw Prof. 0. W. Richardson. 



X 0. W. Richardson and F. C. Brown, Phil. Mag. Sept. 1908; Phil. 

 Mag. Nov. 1908, Dec. 1908, Nov. 1909. F. C. Brown, Phil. Mag. 

 Oct. 1909. 



§ J. S. Townsend, Roy. Soc. Proc. A. vol, 81, p. 464, 



