ELECTRIC RADIATIONS—BRAGG. 209 
locity of the X-ray secondary radiation does not depend on the 
intensity of the X rays. It may be argued that the breadth of the 
pulse is the prime factor, on the grounds that Lenard found the 
velocity of the 6 rays due to ultra-violet hght to depend somewhat 
on the nature of the hght; but it is hard to believe that a diminu- 
tion of the width of the pulse, no matter how extreme, can increase 
the energy of the ejected electron about a thousand times. 
But if we regard the secondary radiation as the result of the 
break-up of a neutral pair, the high velocity of the ejected electron 
(510°) may be more readily explained. The action must be en- 
tirely different from that of ultra-violet light. 
It is difficult to found any arguments for or against either theory 
on considerations of the relative energies of the original cathode 
stream, the X rays, and the secondary rays, for if the energies of 
any transformation do not balance, it is easy to square the account 
by postulating either some release of the internal energy of the atom, 
or the reverse, viz, the absorption of energy by the atom involving 
a disappearance of the visible energy. On the neutral-pair hypothe- 
sis the cathode rays would probably have a trigger action, and the 
pairs would draw their energy from that internal to the atom; it 
might not be necessary to invoke the aid of internal atomic energy 
in order to account for the energy of the secondary radiation. In 
the case of the ether-pulse theory it is necessary to suppose that the 
secondary radiation derives its energy from the atom’s store. (“ Con- | 
duction of 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. Phys., XVIII, p. 991, 1905; 
XXII, p. 793, 1907) and Van der Waals, 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 ether-pulse theory hard X rays are supposed to be thin 
pulses, soft rays to be thick pulses. Swift cathode particles are sup- 
posed to take less time in deflecting and stopping than slower parti- 
cles, 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 dis- 
arrange the pairs less before they are ejected. 
