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LXXVII. Photo-electric Constant and Atomic Heat. By 

 T. Carlton Sutton, B.Sc, Government Research Scholar 

 in the University of Melbourne *. 



rgTHE photo-electric constant, Je, as used in this paper 

 «- is defined (Jeans f) according to the relation 



kv = ^mv 2 + w , 



where \mv 2 is the kinetic energy of an electron driven out 

 of a metal by a radiant beam of wave-length v, and iv 

 (a constant for any particular metal) is the energy required 

 to move the electron from within the atom to a point outside 

 the sphere of action of the atom. 



Hence, kv is the total energy required to expel an electron 

 from the atom with velocity v. 



The figures given in the accompanying table (column 6) 

 show that the values of k do not vary greatly from that of 

 one quantum, namely 6'6 x 10 -27 erg; though there are 

 deviations (the values are invariably low) which have been 

 said to depend in some way on the atomic volume J. 



Some such idea as an indivisible unit or ''quantum" of 

 energy is suggested by the fact that the atomic heats of all 

 elements have approximately the same value ; that is to say, 

 it requires the same amount of heat-energy to change the 

 temperature of any atom a given amount, irrespective of 

 the nature of that atom. 



Here, again,, there are deviations from the mean value 

 6-4. 



When the divergences of the atomic heats are compared 

 with those of the photo-electric constants, a remarkable 

 regularity is noticed. Thus, when the atomic heat is high, 

 the photo-electric constant is low, and vice versa, except in 

 the case of tin and of certain elements of low atomic weight 

 (magnesium, aluminium, cjpper), which show an ano- 

 malously large change of atomic heat with temperature. 

 In these exceptional cases, both values are low at ordinary 

 temperatures, but as the temperature rises the atomic heat 

 increases and the said regularities appear (see Table). 



That this relation holds good is shown in the last column 

 of the table, where the product has been taken of the atomic 

 heat and the photo-electric constant, and has been found to 

 give in almost every case a value close to 35*5. 



* Communicated by Prof. T. R. Lyle, F.R.S. 



t Jeans, " Report on Radiation and the Quantum Theorv," p. 59. 



X Hughes, Phil. Trans. 1912. 



