446 Prof. W. H. Bragg on the Properties and 



It liberates ions in the form of S-rays as it goes, approxi- 

 mately according to the volume law. The /3 ray is also a 

 charged particle, and it is readily to be supposed that it 

 would, if its whole motion were rectilinear, liberate ions 

 according to the same law (comparing atom with atom) as 

 the a particle, though the numbers would be less. But the 

 /3 particle is liable to scattering, and each act of scattering 

 generally implies an increase in the length of the particle 

 in the gas, and increased ionizing power since its speed is a 

 little diminished. Now, scattering is proportional to the 

 atomic weight, whilst the ionization is more nearly propor- 

 tional to the square root of the atomic weight. Thus a heavy 

 atom is the cause of more than its proper amount of ionization ; 

 and so we find in Kleeman's table that the ionizations of the 

 atoms CI, Br, and I are rather higher than in the case of the 

 ol particle. Again, the <y particle is liable to resolution into 

 its elements, with a relatively large amount of ionization. 

 Since this transformation is chiefly effected by impact with 

 heavy atoms, these latter will be the cause of a disproportion- 

 ately large ionization, as compared with the a rays ; and this 

 is also shown by Kleeman's figures. Passing on to X rays, 

 we find a further illustration of this effect, until we come to 

 very soft rays, when we find that the heavy atoms are the 

 occasion of exceedingly large ionization ('Conduction of 

 Electricity through Gases,' 2nd ed. p. 300). There is a 

 good continuity in all these phenomena, with gradual diver- 

 gences just where we should expect them. The a, /?, 7, and 

 X rays all produce the same primary ionization, comparing 

 atom with atom, and differ only in the effects due to scatter- 

 ing and transformation ; that is to say, differ only as regards 

 their production of secondary ionization. Now, the a and 

 (3 rays are certainly material particles, possessing electric 

 fields. There is, therefore, a reasonable argument that the 

 y and X rays are also material, and possess electric fields. 

 This is the case if they are pairs, and the smaller the moments 

 are the more circumscribed are the fields and the less the 

 ionization and the loss of energy. 



If the X rays contain aether pulses only, it is difficult to 

 see why their effects should run so exactly iu parallel with 

 those of the a and /3 rays. 



It has been announced by Marx, as the result of a most 

 ingenious experiment (Phi/s. Zeit. 1905, p. 268), that Pontgeu 

 rays move with the velocity of light. It is extremely im- 

 probable that material particles can possess such a velocity : 

 and the experiment of Marx might seem at first sight to be 

 strongly against any material nature of the X rays. But it 



