On the polarisation of X-rays compared with their power of exciting high velocity cathode rays

1. The discovery of polarisation of Röntgen rays was suggested by the ether pulse theory, and gave this theory a good support. But, on the other hand, the theory meets with many difficulties when we are going to account for a number of other properties of these rays which recent investigation has brought to light. Sir J. J. Thomson has tried to make the ether pulse theory consistent with observations by introducing new properties for the pulse-medium, and assumes that the ether has a structure, and that the energy radiating from the pulse centre is transmitted along “lines of force” with undiminished intensity. Prof. W. H. Bragg has assumed, in the so-called “neutral pair theory,” that the rays are of a corpuscular nature. For a fuller discussion of the arguments in favour of this view I must refer to Prof. Bragg’s papers. I shall here confine myself to mentioning that one of the chief difficulties on the ether pulse theory is to explain the properties of secondary cathode rays, as the latter, on account of the relation existing between their velocity and the hardness of the bulb, must be supposed to get their energy from the exciting X-rays. What may be said to offer some difficulty to the neutral pair theory is the existence of polarisation, and although Bragg has called attention to the fact that the neutral pairs possess all properties which are necessary to produce asymmetric phenomena of the kind termed polarisation, there still remains some difficulty in explaining that the polarisation is able to make itself felt already in the primary beam, and to explain why certain directions of spin of the doublet should be more likely to occur than others.