166 Prof. Richardson and Mr. Robertson : Effect of 



less sensitive to the admission of hydrogen, and this condition 

 persisted after the tube had been baked out in the furnace 

 and re-exhausted. Typical curves at this stage under differ- 

 ent pressures are shown in figs. 4 and 5. Although the 



Fi* 



VOLTS SHIFT TOWARDS NEGATIVE. 



«OS '12 '16 'Z> °14 



■56 



31 



displacements are small a careful examination of all the data 

 strongly suggests that they are real. The position of the 

 point on the voltage axis for which the current had half 

 the saturation value is given for a series of pressures in the 

 following table : — 



Pressure (mm. X H) 4 ) . 

 Voltage for half value. 



> l 



17 



-•30 



65 4.63 



-•35 --41 



1000 

 -•45 



It will be seen that the voltage displacements for a given 

 increment in pressure are greater when the pressure is low. 

 This condition, of which figs. 4 and 5 are typical examples, 

 appeared to be stable and persisted to the end of the experi- 

 ments, in the course of which the wire was heated some 

 hundreds of hours. The displacements on reducing the pres- 

 sure were generally somewhat smaller than those obtained 

 .when the pressure was increased between the same limits. 



