PHYSICS 



19 



as to the precise correspondence between the charges on the 

 nuclei of the atoms in the periodic table and the first ninety- 

 two ordinal numbers. 



The situation, however, as regards the next important 

 problem of atomic structure, viz. the positions of the planetary 

 electrons, is not so satisfactory. On this point the evidence has 

 mostly been drawn from spectroscopy and chemical statics, 

 and unfortunately the results derived from these two classes of 

 data have been rather discordant. The great advantage of the 

 chemical data lies in the fact that they refer to a few electrons 

 in the atom, they have a qualitative as well as a quantitative 

 significance, and, most important of all, they give evidence on 

 the structure with very little reference to the difficult question 

 of atomic dynamics except in its statical aspect. Spectroscopic 

 data, on the other hand, while they deal with one electron at a 

 time, involve complicated corrections due to all the other 

 electrons in an atom, and can only be elucidated with reference 

 to some system of atomic dynamics. Such a system we do not 

 possess at present except in an embryonic form ; for if there is 

 one thing which is certain nowadays, it is that the classical 

 dynamics of Newton, Lagrange, and Hamilton and the electro- 

 dynamics of Maxwell are inadequate to explain the movements 

 within the microcosmic systems we call atoms. 



From the point of view of statics alone we have all the facts 

 of chemical combination and action, e.g. the tetrahedal form of 

 the carbon atom, the periodic table, and also the information 

 concerning the structure of crystals derived by the methods of 

 X-ray analysis. All this points to a type of structure first 

 suggested by G. N, Lewis and worked out in greater detail 

 by Langmuir, and strongly supports a system of atomic statics 

 proposed by Parson. One of the most important facts to which 

 this theory appeals is the numerical position in the periodic 

 table of the inert gases. Thus Helium is the second, Neon 

 tenth. Argon eighteenth. Krypton thirty-sixth. Xenon fifty- 

 fourth, Niton (Radium Emanation) eighty-sixth. Now 2 = 

 2 X i^ 10 = 2 X (i'- + 2=), 18 =2 X (1= + 2^ + 2'), 36 = 

 2 X (i'' + 2' + 2' +3'), 54 = 2 X (i' + 2* +2' +3; +3'), 86 

 = 2 X (i* +2^ +2^ +3* +3* +4^). Following this clue, it 

 is suggested that the space occupied by the atom can be con- 

 ceptually divided into spherical shells and each shell divided 

 into compartments or " cells." In the first shell, which will be 

 a spherical space immediately surrounding the relatively 

 minute nucleus, there will be two (hemispherical) cells. The 

 next shell (lying between two spheres) will have four times the 

 volume of the first and will contain 8 ( =2 x 2=) cells of the 

 same volume as those in the first shell, these cells most probably 

 corresponding to octants of the outer sphere. The third shell 



