510 Sir J. J. Thomson on the Structure of 



position of the apses in the bipole orbits show that H does^ 

 penetrate into these regions. So it is really only possible to 

 put the argument in very vague form and to say that there 

 appears to be no obvious characteristic of fig. 10, which. 

 would suggest that the bipole should have a more plate-like 

 effect than the square nucleus. 



11. Conclusion. 



The comparison of any theoretical collision relation with 

 experiment is a very exacting test, for it is a comparison of 

 relations between three variables, and there is only one 

 adjustable constant, the diameter of the nucleus. All the 

 others, masses, charges, and velocity of approach are known 

 from other work. Comparing fig. 9 with figs. -1 and 5, 

 a rough measure of agreement was found with a nucleus 

 of diameter 2'7 x 10 _lb cm., but in view of the doubt that 

 has been thrown on the experiments not much confidence 

 can be placed in this. It is better to leave the decision as 

 to the shape and size of the nucleus, until accurate experi- 

 ments are made. One point of very great interest may. 

 however, be noted as a possibility. Should future experi- 

 ments confirm the flatness of curve A in fig. 4, it would be 

 very strongly suggestive of the type of collision relation 

 exhibited in fig. 7 : that is to say, it would indicate that 

 there was a discontinuity in the law of force between the 

 nuclei. 



XLV. On the Structure of the Molecule and Chemical 

 Combination. By Sir J. J. Thomson, O.M., F.B.S. * 



FROM many points of view the structure of the molecule 

 is even more important than that of the atom. For- 

 the structure of the molecule involves the method by which 

 the atoms are linked together to form stable systems of 

 different kinds, and is thus at the root of the enormously 

 important question of chemical combination. In fact 'the 

 extension of the electronic theory of matter to chemistry 

 depends upon the solution of the problem of the structure of 

 the molecule. 



Regarding an atom as a stable arrangement of a mixture 



* Communicated by the Author. 3Iany of the results in this paper 

 were given "by me in my lectures at the Royal Institution between 1914 

 and 1919, but owing- to the pressure of other duties I have not hitherto 

 had leisure to prepare them for publication. 



