[ 735 ] 



LXXYII. On the Carriers of the Negative Thermionic Current 

 in a Vacuum. By Gwilym Owen, M.A., D.Sc, and 

 Robert Halsall, B.Sc, University of Liverpool *. 



IT has long been known that electricity o£ both signs is 

 discharged from incandescent bodies. The current so 

 obtained from a charged wire to the surrounding electrode 

 is called by 0. W. Richardson a thermionic current, and 

 the carriers are called thermions. Workers in this field are 

 not yet agreed as to the nature of the positive thermions, 

 but it has been established by various observers that the 

 negative carriers in a vacuum are mainly free electrons. 

 Sir J. J. Thomson f in 1$99 measured e/m for the negative 

 thermions from a carbon filament at low pressure and 

 obtained the value 10 7 . Values of the same order have 

 since been obtained by Wehnelt J for the negative thermions 

 from hot lime, and by wen for those from platinum § and 

 the Nernst filament ||. 



Now it is well known that metal wires contain considerable 

 quantities of absorbed gases which are evolved at a high 

 temperature. Moreover, some substances — carbon and pal- 

 ladium, for example — disintegrate H rapidly when raised to 

 incandescence at a low pressure. The question therefore 

 arises : Is the negative thermionic current conveyed solely 

 by electrons or by an admixture of electrons and heavy 

 gaseous or metallic ions? 



This point was investigated, in the case of platinum, by 

 one of the writers in 1904 (Proc. Camb. Phil. Soc. loc. cit.)* 

 The results then obtained led to the conclusion that at tem- 

 peratures below 1000° 0. the negative thermionic current is 

 conveyed solely by electrons, while at higher temperatures 

 there appeared evidence of the presence in the discharge of 

 a small percentage (about 5 per cent.) of heavy ions. 



The writers have recently re-examined this question us 

 to the presence of heavy ions in the negative thermionic 

 current, and the present paper is a short account of the 

 results obtained. The metals studied have been palladium, 

 pure and commercial platinum, and iridium, and were in the 

 form of wires about 0*4 mm. diameter. The method of 

 investigation was, in the main, identical with that used 



* Communicated by the Authors. 



t Thomson, Phil. Mag. [5] vol. xlviii. p. 547 (1899). 



% Wehnelt, Ann. d. Phys. vol. xiv. p. 425 (1904). 



§ G. Owen, Proc. Camb. Phil. Soc. vol. xii. p. 493 (1904). 



I! G. Owen, Phil. Mao-. [6] vol. viii. p. 230 (1904). 



% J. H. T. Roberts, Phil. Mag. February 1913. 



