﻿Thermionic Currents from Tungsten. 803 



have secondary effects, but would not be required to explain 

 the existence of the current. 



In view of some recent experiments *, which seemed to 

 <3ast doubt upon the above explanation of thermionic currents, 

 the following investigation was undertaken. Professor 

 Richardson has already published the results of the earlier 

 -experiments f. The object has been (1) to make a detailed 

 quantitative investigation of the negative thermionic emission 

 from tungsten over a large temperature range, and (2) to 

 discover, if possible, more evidence as to the conditions 

 which determine the emission. 



Experimental Arrangements. 



The filaments used in these experiments were all taken 

 from a spool of pure ductile tungsten furnished by the 

 General Electric Co., Schenectady, N.Y. They were 

 0*041 mm. in diameter, and the lengths used in the different 

 lamps varied from 2*5 cm. to about 9 cm. They were 

 electrically welded in hydrogen to copper leads, which, in 

 turn, were welded to platinum wires. Then the wires were 

 mounted axially in cylindrical glass tubes and sealed in. 

 The tubes were 3*2 cm. in diameter, and contained copper 

 gauze cylinders 2' 6 cm. in diameter. Separate wires con- 

 nected these anodes to the outside of the lamps. 



Fig. 1. 



Fio-. 1 shows the arrano-ement for exhausting and heating 

 the lamp L, in the vacuum furnace. The figure is purely 

 diagrammatic and is not drawn to scale. The U-tube, U, 



* Pring and Parker, Phil. Mag-, vol. xxiii. p. 192 (191 2) ; Prill?, Proc. 

 Hoy. Soc. London (A.), vol. lxxxix. p. 844 (1918) ; Fredenhagen,ZteutocA. 

 Pkt/s. Gesell. Verh. vol. xiv. p. 384 (1912). 



t Richardson, Phil. Mag. vol. xxvi. p. 345 (1913). 



a F2 



