Radiation and the Structure of the Atom, 395 



application of the Quantum theory o£ radiation to the theory 

 of the nucleus atom. As the theory has been made a subject 

 of criticism, and as experimental evidence of importance 

 bearing on these questions has been obtained in the mean- 

 time, an attempt will be made in this paper to consider 

 some points more closely. 



§ 1. General assumptions. 



According to the theory proposed by Sir Ernest Rutherford, 

 in order to account for the phenomena of scattering of a-rays, 

 the atom consists of a central positively charged nucleus 

 surrounded by a cluster of electrons. The nucleus is the 

 seat of the essential part of the mass of the atom, and has 

 linear dimensions exceedingly small compared with the 

 distances apart of I he electrons in the surrounding cluster. 

 From the results of experiments on scattering of alpha 

 rays, Rutherford concluded that the charge on the nucleus 

 corresponds to a number of electrons per atom approxi- 

 mately equal to half the atomic weight. Concordant 

 evidence from a large number of very different phenomena 

 has led to the more definite assumption that the number 

 of electrons per atom is exactly equal to the atomic number, 

 i. e., the number of the corresponding element in the periodic 

 table. This view was first proposed by van den Brock *. 

 Whilo the nucleus theory has been of great utility in 

 explaining many important properties of the atom f, on the 

 other hand it is evident that it is impossible by its aid 

 to explain many other fundamental properties if we base 

 our considerations on the ordinary electrodynamical theory ; 

 but this can hardly be considered as a valid objection 

 at the present time. It does not seem that there is any 

 escape from the conclusion that it is impossible to account 

 for the phenomena of temperature radiation on ordinary 

 electrodynamics, and that the modification to be introduced 

 in this theory must be essentially equivalent with the 

 assumptions first used by Planck in the deduction of his 

 radiation formula J. These assumptions are known as the 

 Quantum theory. In my previous paper it was attempted 

 to apply the main principles of this theory by introducing 

 the following general assumptions : — 



* van den Bvoek, Phys. Zeit, xiv. p. ?>'I (1913). 

 t See Rutherford, Phil. Mag. xxvii. p. -188 (191-1). 

 t See J. II. Jeans, " lleport on Radiation and tie Quantum Theory, 7 

 Phys. Soc. London, 1914. 



