the Corpuscular Hypothesis of the y and X Rays. 389 



the new hypothesis, with the consequent abandonment of the 



spreading pulse theory. Only one thing o£ value : viz. the 



easy explanation of the partial polarization of a primary beam 



of X rays, and of the more complete polarization of secondary 



beams. Those who would maintain that the entity contains 



a wave-motion within it might argue that there is no loss of 



© © 



this kind ; but such a position would seem unsound until 

 there is a clear expression of the meaning and properties of 

 an entity or bundle of energy with a wave-motion inside it. 

 It is to be observed that the polarization of light is a very 

 complex phenomenon which is capable of the closest exami- 

 nation, and that the undulatory theory of light explains it 

 with great exactness. It is possible to overrate the im- 

 portance of the ability of the pulse theory to explain the 

 polarization of X rays, because it may be imagined that in 

 this case also a complex effect i& successfully accounted for. 

 As a matter of fact the polarization of X rays is quite a 

 simple effect and bears but a meagre resemblance to the 

 polarization of light; there are, for example, none of the 

 elaborate and beautiful effects of crystals. The polarization 

 of the X ray consists only in the fact that if it is deflected it 

 is more liable to move in one particular plane passing through 

 its line of flight than in another : a billiard ball with side on 

 does as much, or more exactly still, a spinning tennis ball. 



If we accept the entity hypothesis the processes of the 

 X-ray tube assume a new aspect. We gain in precision of 

 statement and in clearness of outlook. The stream of cathode 

 rays is directed against the anticathode ; we no longer say, 

 somewhat vaguely, that part of the energy goes in heat, part 

 in secondary cathode radiation, part in X rays. We must 

 not imagine a cathode ray to ricochet hither and thither 

 among the atoms of the anticathode radiating X-ray energy 

 at every turn. No doubt it does so- radiate some energy, but 

 the amount is trifling,, and has nothing to do with X rays. 

 We must rather say, that when each cathode particle strikes 

 the anticathode it may fritter away its energy into a form 

 which finally takes that of heat, or it may be splashed back 

 against the glass wall of the tube r and cause phosphorescence 

 and other effects, or, again, it masy disappear (not necessarily 

 at its first meeting with an atom, nor before it has spent any 

 of its energy) , and the complete disappearance of the cathode 

 ray as such will then be simultaneous with the production of 

 the X-ray entity. In the last case the entity starts off on 

 its straight line course endowed with a penetration which 

 the cathode ray did not possess. When it meets an atom, 



