734 Mr. J. Chad wick on the Charge on the 



compounds of the type C . H . HO, E l5 R 2 > the system of 

 coupling electrons will tend to twist round the line joining 

 the electrons which couple H and OH with the carbon 

 atom. 



The other condition for optical rotation is geometrical 

 asymmetry. The electrons cannot be at the corners of a 

 regular tetrahedron, and this arrangement, which is the one 

 usually asssuined, is incompatible with optical rotation. 

 The departure of the molecule from this form, in fact the 

 shape of the molecule, is of vital importance in connexion 

 with optical rotation, but on this subject little, if anything, 

 seems to have been done. 



If we had a theory which gave the configuration of the 

 molecule and the periods of vibrations of the electrons, we 

 could calculate by the expression given above the value of 

 the molecular rotation. Inasmuch as the configuration and 

 periods enter into these expressions in a complicated way, 

 the effect of any one period, for example, depending on its 

 relation to each of the other periods, the periods are not 

 easily calculated from the rotation. Thus observations on 

 the optical rotation are more likely to be useful as a test of 

 any theory of the configuration and structure of the molecule 

 than as a means of discovering this structure. 



Since the above was written I have seen a paper by Stark 

 (Jaltr. f. Eadioaldivitat, xi. p. 194, 1914), in which the 

 subject of optical rotation is also treated from the point of 

 view of the electron theory ; the treatment is wholly' quali- 

 tative, and I find it difficult to follow the reasoning ; so far 

 as I am able to do so it seems to me to be fundamentally 

 different from that given above. 



LXXXIV. The Charge on the Atomic Nucleus and the Law 

 of Force. By J. Chad wick, M.Sc, Wollaston Student of 

 Gonville and Caius College, Cambridge*. 



§ 1. rjlHE theory of the nuclear constitution of the atom, 

 JL put forward by Sir Ernest Rutherford f in 1911, 

 has been confirmed by evidence gathered from such various 

 sources that it now forms the foundation on which the 

 development of atomic physics is based. On this theory, 

 the positive charge associated with an atom is concentrated 

 on a massive nucleus of small dimensions, surrounded 



* Communicated by Professor Sir E. Rutherford, F.P.S^ 

 t Rutherford, Phil. Mag-, xxi. p. 6(39 (1911). 



