wlien an Electron escapes from Surface of a Hot Body. 213 



It is difficult to make any definite statement as to the 

 exact accuracy of the above measurements because of some 

 apparently unavoidable errors., In the cases of tungsten 

 and tantalum the galvanometer was subject to slow drifts, 

 sometimes in one direction and sometimes in the other. It 

 is thought that these drifts were caused by a lack of homo- 

 geneity in the filaments. A tungsten filament when passed 

 between steel rolls broke up into five or six finer filaments. 

 It may be that these wires are never quite homogeneous. It 

 is thought that errors of this sort are largely eliminated from 

 the mean. For tungsten the mean variation from the mean 

 of the eighteen values found was "11 volt or 2 per cent. 

 It is thought that this represents about the accuracy for the 

 tungsten and tantalum measurements. Owing to the lack of 

 ideal conditions for carbon and to the fact that the small 

 temperature-resistance coefficient caused the galvanometer 

 deflexions to be small, the carbon values are probably not 

 accurate within less than 4 per cent. Only one specimen 

 of molybdenum was examined. The readings were good, 

 however, and may be regarded as accurate within the same 

 limits as the values for carbon. 



It is interesting to note in this connexion that values of cf> 

 found for one wire that was known to be not homogeneous 

 were more nearly normal than were corresponding values 

 of " b " found by observing the temperatures and currents. 

 From this observation it was concluded that measurement 

 of the value of <f> is less subject to error than are corre- 

 sponding measurements of the value of " 5." It may be 

 that the value of b can be more accurately determined from 

 the cooling effect than it can be from the current-temperature 

 relationship. 



III. Certain Features related to the Problem. 

 1. Identification ofb ivitli cf>. 



It will be remembered that in the theoretical derivation 

 of the Richardson equation, b is supposed to represent the 

 work done when an electron escapes from the surface. Since 

 this work is measured by the potential difference represented 

 by </>, it follows that b and $> should be equivalent if the 

 assumption in regard to b is correct. 



The relationship between <£ and b should be given by 



b = t • • (') 



where e is the charge on an electron and R is the gas 

 constant calculated for a single molecule. 



