﻿802 Mr. K. K. Smith on Negative 



The main object of this paper is to show that the form of 

 quantum-theory which seems necessary to account for line 

 spectra is not really distinct from that originally proposed 

 by Planck, and the subject of its further application to line 

 spectra and other phenomena may be left for a future 

 publication. 



In conclusion I wish to express my thanks to Professors 

 J. W. Nicholson and 0. W. Richardson for their advice and 

 criticisms. 



Wheatstone Laboratory, King's College, 

 March 1915. 



LXXXIV. Negative Thermionic Currents from Tungsten. 

 By K. K. Smith, A.B., Fellow in Physics, Princeton 

 University *. 



Introduction. 



ri^HE emission of negative electricity from an incandescent 

 JL metal or carbon filament has been the subject of several 

 investigations f. The number of electrons carried from the 

 filament to a neighbouring positively charged electrode 

 increases very rapidly with the temperature. The exact 

 quantitative relation between the number of electrons emitted 

 -and the temperature of the filament was established by 

 Richardson, and has been verified by the experiments of 

 others. It was assumed that the emission is determined 

 simply by the number of electrons whose kinetic energy is 

 sufficient to overcome the forces tending to prevent their 

 escape from the metal. 



This relation is expressed by the formula 



i = aT 2 e~T i 



where i is the saturation (maximum) current in amperes per 

 square cm. and T is the absolute temperature. The quantities 

 a and b are constants, the latter being proportional to the 

 work done by an electron in escaping from the metallic 

 surface. On this view, a pure metal in a perfect vacuum 

 would give a thermionic current which would be a function 

 of its physical properties only. In any actual case the 

 presence of traces of impurities or gases would presumably 



* Communicated by Prof. 0. W. Richardson, F.R.S. 



t Richardson, Camb. Phil. Proc. vol. xi. p. 286 (1901) ; Phil. Trans. 

 A, vol. cci. p. 497 (1903) ; H. A. Wilson, Phii. Trans. A, vol. ccii. p. 243 

 (1903) ; Deininger, Ann. d. Pnys. xxv. p. 304 (1908). 



