Natures of various Electric Radiations. 445 



Electricity through Gases/ p. 321). It is not clear whether 

 such a call must also be made at the transformation of cathode 

 into X rays. The whole question, taken into conjunction 

 with the diffraction experiments of Haga and Wind, has 

 lately been under discussion by Wien (Ann. d. P/njs. xviii. 

 p. 991, 1905 ; and xxii. p. 793, 1907) and van derWaals, Jr. 

 (Ann. d. Phys. xxii. p. 603, 1907) : but no definite conclusion 

 is reached. 



It is not easy to see how the irregular stoppage of the 

 cathode particles can give rise to pulses of sufficient definition 

 and uniformity to show diffraction. It would be easier to 

 explain such an effect as the result of uniform disturbances 

 arising when pairs of uniform nature are torn from the atoms 

 of the anode. 



On the sether-pulse theory hard X rays are supposed to be 

 thin pulses, soft rays to be thick pulses. Swift cathode 

 particles are supposed to take less time in deflecting and 

 stopping than slower particles, and therefore to give rise 

 to thinner pulses. On the other theory we must suppose 

 that the rays are hard when the moments of the pairs are 

 small : or possibly that hardness is due to high velocity. If 

 the former is the case, it may be that fast cathode particles 

 spend less time within the anode atoms than the slow ones 

 do, and therefore disarrange the pairs less before they are 

 ejected. 



There is another entirely different argument, which seems 

 to support the neutral-pair hypothesis. 



The a, /3, and y rays all ionize the gases which they tra- 

 verse. It has just been shown by Kleeman * that the 

 ionization per atom due to j3 and <y rays is nearly propor- 

 tional to the ionization per atom due to a rays (and, there- 

 fore, approximately proportional to the volume as I have 

 shown, Proc. Roy. Soc. of S. A., Oct. 1906 ; Phil. Mag. 

 March 1907). The figures for the heavier atoms are rather 

 larger for the /3 than the a. rays, and still larger for the 

 7 rays. It is known that the ionizations due to X rays 

 differ considerably from those due to y rays 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 « particle first, since 

 its circumstances are the most simple. It moves directly 

 through the atoms, without scattering or transformation. 



* Mr. Kleeman has been good enough to inform me of his results by 

 letter; but I believe I am at liberty to quote them, since he has, 1 under- 

 stand, recently read a paper on the subject before the Royal Society. 



Phil, Mao. S. 6. Vol. 11. No. 82. Oct, 1907. 2 H 



