586 Prof. 0. W. Richardson and Mr. K. T. Compton on 



which determines the slope o£ the individual curves, they are 

 collected together in the following table : — 



Metal. 



Values from Tm. 



Values from TV. 



iV 



K 



km. 



v . 



K 



k r . 



2-6 



2-6 



2-55 



2-8 



2-75 



1-9 



1-65 



2-8 



N a 



51-5 

 63 



78-5 



80 



83 



91 

 100 

 104 



58-3 



47-7 



38-2 



37-6 



36-2 



33 



30 



28-8 



5-2 



4-3 



5-2 



5-1 



49 



3-55 



3-8 



5-85 



52 

 73 

 80 

 84 

 89 

 89 

 97 

 103 



57-7 

 411 

 37-5 

 35-7 

 337 

 33-7 

 309 

 291 



Al 



Ms 



Zn 



Sn 



Bi 



Cu 



Pt 





The unit for \ is 1 = 10 6 cm. and for Jc m and h 

 1 = 10" 27 erg sec. 



The values of X given by the mean energy T r are practically 

 identical with those given by the maximum energy T TO except 

 in the case of aluminium. When the two differ we are in- 

 clined to attach more weight to the values from T r for the 

 reasons already stated. 



Some years ago Einstein * showed that it followed from 

 the unitary theory of light that the maximum energy T m of 

 the electrons emitted under the influence of light should 

 satisfy the equation 



T TO = Av-P, (8) 



where v is the frequency of the light, h is Planck's constant, 

 and P the work which the electrons have to do in order to 

 escape from the material. One of the writers | has recently 

 shown that T m and T r have to satisfy the equations: — 



T m =hv — w , (9) 



T r = 8 (hv-w ) ..... (10) 



where w is the latent heat of evaporation of the electrons, 

 per electron, at the absolute zero of temperature, and s is a 

 quantity which depends upon the reflexion of electrons at 

 the surface of the material. The precise definition of s is as 

 follows. Consider the surface in question to form part of an 

 isolated system in thermal equilibrium. It will be continually 



* Ann. der Physik, vol. xvii. p. 146 (1905). 



t O. W. Richardson, Phys. Rev. vol. xxxiv. pp. 146, 384 (1912) ; 

 Phil. Mag. vol. xxiii. p. 615 (1912) ; Science, vol. xxxvi. p. 57 (1912). 



