3o8 SECTIONAL TRANSACTIONS— A. 



of the completion of the M shell. In this way we obtain the successive 

 structures shown in the table : 



n p n I 



HI H^ He^ He* | K shell 



Inpnpnpnpnp n pi 



He^ Li« Li' Be^ Be» B'" B" C^^ C" N^* N^^ O^^ | L shell 



Innppn n p p n n 



017 018 F^" Ne^" Ne^i Ne^^ Na^^' Mg^* Mg^^ Mg^e 



ppn nppn n p P| 



Al^' Si^s Si^^ Si^" P" S32 S" S34 CP5 A^" I M shell 



All these are known except He' and He^. Apart from these two excep- 

 tions these isotopes, and only these, occur for masses below 37. We might, 

 of course, have closed the ' K shell ' at H^ and started reversing the order 

 of alternate addition at that point. This would make the third member 

 H' instead of He^. Above 36 the rules are evidently more complicated. 



I feel confident that the regularities exhibited in the table represent 

 something important. (In the unlikely event of this not being the case, 

 at least they give a convenient way to remember all the isotopes below 37.) 



I was glad to hear that Dr. Chadwick regarded the neutron as some kind 

 of a combination of a proton and an electron. Some authorities with whom 

 I have discussed the matter seem disposed to look upon it as some entirely 

 new kind of ultimate structure. The only advantage that this seems to 

 confer is that it might afford a way of accounting for the inconvenient 

 abnormal nuclear spin of a body like N^*. I feel that this is too small a 

 matter to invoke an entirely new material entity to account for, and that the 

 abnormal spin is probably due to something else. There is no known 

 a priori reason why any such new entity should have any particular mass, 

 at any rate not a mass approximating to that of H^. The occurrence of 

 an entirely new entity with a mass just under that of H^ seems to me so 

 improbable that, until some new reasons in favour of it are put forward, it 

 is hardly worthy of serious consideration. 



Dr. N. Feather. 



Experiments were described in which the expansion chamber was used 

 to study the disintegration of nitrogen and oxygen by neutrons. It seems 

 that the disintegrations are not all of the same type. In many cases the 

 neutron is captured and an a-particle ejected ; in others the neutron is not 

 captured and the ejected particle may be a proton. 



Mr. P. L Dee. 



The author described experiments to examine the collisions of neutrons 

 with electrons. These are extremely rare, even compared with the nuclear 

 collisions : not more than one such collision occurs in a path of 3 metres 

 in air. 



Mr. T. Smith. — Hamilton and aplanatism. 



Afternoon. 

 Visit to the works of Messrs. Cooke, Troughton & Simms, Ltd. 



