168 Prof. Richardson and Mr. Robertson : Effect of 



emission from platinum in the 'Emission of Electricity frorr 

 Hot Bodies,' Chap. iv. pp. 108 et seq., to which the following 



Fiiv 5. 



VOLTS. 



references relate, in general (equation 34' p. 109), the 

 contact potential difference between any two surfaces at 

 temperature Tx is 



Vi=— log--, = — log ? , . . • • (1) 



where i and i' are the saturation currents per unit area of the 

 two surfaces at 1\. If the dashed variables refer to the clean 

 metal and the undnshed to the metal in presence of gas, it 

 follows from (13) p. 112 that 



ili'^(l + ap c )^- 1 ) j .... (2) 

 whence 



Vi= ?(i- 1 ) ,og(1+a ^- •.'■'■" (3) 



