198 Profs. Richardson and Cooke on the Heat developed 



should, to the true zero of average voltage. Along the part 

 of the curve which corresponds to approximate saturation 

 the deviation from linearity cannot be detected. But where 

 the current is far from saturation the points on it lie very 

 considerably above the straight line, so that in this region a 

 considerable error would be introduced by supposing that 

 the average energy of the thermions emitted by the filaments 

 corresponded to what they would gain if they all fell through 

 a difference of potential equal to that at the middle of the 

 filament. Practically all the observations which have been 

 made fall within the part of this curve where the deviation 

 from the linear relation is less than the error of observation. 



§ 13. Corrections. 



(1) For the Temperature Energy of the Electrons. 

 We have seen that the heating effect for zero applied 

 voltage consists of two parts, (1) the part which we are 

 measuring due to the difference of the potential energy of 

 the electrons inside and outside the metal, and (2) a part 

 which is equal to the difference between the kinetic energy 

 of thermal agitation of the electrons as they are emitted 

 from the hot metal and the value which that quantity would 

 have at the temperature of the grid. Thus, if 6 X is the 

 temperature of the osmium filament and 2 that of the grid, 

 this part of the heating effect will be equal to 



(e 1 -6 ) = " c '(A-e ), 



where // is the number of molecules in a cu. cm. of gas under 

 standard conditions of temperature and pressure. 

 Then wax273 



= the tran slational kinetic energy in 1 cu. cm. of EL at 



0°C. and 760 mm. 

 = |p = |x 76 x 13*6 x981 x 10 ~ 7 joule. 

 ne = charge carried by ^ cu. cm. of H 2 in electrolysis 

 = 4*327 coulombs. 



Let us assume, what is approximately correct, that the 

 temperature of the osmium is 2000° C. above the temperature 

 of the grid. Then substituting the above values, we find 



-(0 1 -0 o ) = -25 volt. 



It is necessary, therefore, to subtract this amount from the 

 observed value of the heating effect in order to deduce the 

 part which depends on the change in the potential energy. 



