214 Mr. H. H. Lester : Determination of Work Function 



It is important that the equivalence of c6 and b be estab- 

 lished in order that the validity of the Eichardson equation 

 should be more completely demonstrated, and also for another 

 reason. The assumption involved in 5 rests upon the further 

 assumption that the transnational kinetic enorgy of an elec- 

 tron in a hot metal is equal to the energy of a gas molecule 

 in a gas at the same temperature as the hot metal. This 

 latter supposition has been proved true by the experiments 

 of Eichardson and Brown *. Their work receives additional 

 support if it is demonstrated that <£ and b measured inde- 

 pendently are shown to be equivalent. The term -(#1— #o) 



in the expression for <j> is based upon the results of Eichard- 

 son and Brown's work. However, as pointed out elsewhere, 

 this term contributes but little to the value of (f>, so that its 

 presence does not seriously affect the validity of the check. 



The experimental verification of equation (7) was attempted 

 by Eichardson and Cooke, but, as explained above, their 

 values of </> obtained from the heating effect were of insuffi- 

 cient accuracy to give more than an approximate test. Their 

 work on tungsten, however, was carried out under ideal con- 

 ditions and by a method that is capable of giving accurate 

 results. They found for tungsten 



$ = 4*24 eq. volts, 



from which, by eq. (7) 



b = 49400. 



Langmuir f has determined b very accurately for the same 

 metal, and has found 



b = 52500. 



Eecent work in this laboratory by Dr. K. K. Smith J gives 



b = 54700. 



Dr. Smith's value v«as obtained as the mean of a large 

 number of determinations in which high and low values are 

 given equal weight. It is probable that the low values are 

 more nearly correct. If Langmuir's value is given weight 2 

 and Smith's weight 1, then the weighted mean of the two 

 determinations gives 



b = 53600. 

 The Cooke and Eichardson value as calculated from <£ differs 



* Phil. Mag. vol. xvi. p. 353 (1908). 



t Phvs. Kev. Dec. 3913 ; Phys. Zeit. vol. xv. p, 516 (1914). 



X Phil. Mas-. June 1915. 



