97 



when the X-rays are soft; but approximate to them when the 

 X-rays are hard. 



All this fits in excellently with the theory that all four 

 types of rays are material. Take the a particle first, since its 

 circumstances are the most simple. It moves directly through 

 the atoms, without scattering or transformation. It liberates 

 ions in the form of S rays as it goes, approximately according 

 to the volume law. The /? 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 (com- 

 paring atom with atom), as the a particle, though the num- 

 bers would be less. But the (3 particle is liable to scattering, 

 and each act of scattering generally implies an in- 

 crease in the length of the particle in the gas, 

 and increased ionising power since its speed is a 

 little diminished. Now, scattering is proportional to 

 the atomic weight, whilst the ionisation is more 

 nearly proportional to the square root of the atomic 

 vveight. Thus, a heavy atom is the cause of more than its 

 proper amount of ionisation; and so we find in Kleeman's 

 table that the ionisation of the atoms CI, Br, and I are rather 

 higher than in the case of the a particle. Again, the y particle 

 is liable to resolution into its elements, with a relatively large 

 amount of ionisation. Since this transformation is chiefly 

 effected by impact with heavy atoms, these latter will be the 

 cause of a disproportionately large ionisation, 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 

 lieavy atoms are the occasion of exceedingly large ionisation 

 (Conduction of Electricity through Gases, 2nd Ed., p. 300). 

 There is a good continuity in all these phenomena, with 

 gradual divergences just wliere we should expect them. The 

 a, /?, y, and X-rays all produce the same primary ionisation, 

 comparing atom with atom, and differ only in the effects due 

 to scattering and transformation ; that is to say, differ only as 

 regards their production of secondary ionisation. 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 mo- 

 ments are the more circumscribed are the fields and the less 

 the ionisation and loss of energy. 



If the X-rays contain ether pulses only, it is difficult 

 to see why their effects should run so exactly in parallel with 

 those of the a and /S rays. 



As I have already pointed out, the neutral-pair theory 



