when an Electron escapes from Surface of a Hot Body. 199 



electrode than the heating effect at the surface of the cold 

 one *. 



The rate of production of heat by a current i flowing 

 across the boundary of the cold electrode is given as 



;(<2>+v+^ (0,-0,,)), 



where cf) represents the equivalent potential at the surface, 

 V the potential between the electrodes, 

 a twice the gas constant calculated for a single 



molecule, 

 e the charge on an electron, 



1 and 6 the absolute temperatures of the hot and 

 cold electrodes respectively. 

 i is the saturation current and is independent of V. 

 The 0's are constant ; hence the expression inside the 

 parentheses is a linear function of V. The heating effect 

 was measured by comparing the change in resistance 

 produced by the influx of electrons with that produced 

 by a known increment of current through the metal 

 of the electrode. The effects thus found for a series of 

 voltages were plotted against V, and the intercept of the 

 straight line thus found with the heating-effect axis gave 

 the value per unit current of 



4>+- e {ev-e <1 ) = h ; 



from which 4> = R _«_ {0i _ eo) . 



The materials under investigation were mounted in thin 

 strips forming a grid between two osmium filaments which 

 served as the hot cathode. The electrodes were mounted in 

 a brass vessel that was made airtight by means of waxed 

 joints. It was impossible to observe in such an arrangemnt 

 the precautions that Langmuir has since shown to be necessary 

 to insure consistent behaviour of thermionic phenomena. 



Their results showed that small changes in the gas-pressure 

 did not affect the value of <j>. Evidence was found to support 

 a theory put forth by Richardson that the heating effect 

 is a function of the cooling effect through the relationship 



W 1 = W ! +eV 0) 



or in terms of <£, 



<£i = $2 + V c , 



where Y c represents the contact potential between the hot 



* 0. W. Richardson, u Rapports du Congres Iut. de Radiologie," 

 Brussels, 1910. 



