200 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
The existence of a common speed for all 8 rays may, of course, 
imply that the ejection is not directly effected by the ionizing agent, 
but that the latter simply precipitates the discharge. A man running 
through a battery might pull the triggers of some or all of the guns 
which it contained, and the velocity of the shot would not depend on 
the strength of the man, nor the rate at which he ran, nor how much 
energy he spent in the transit. And so it may be understood why 8 
rays are projected at a speed which is independent of the nature of 
the agent, as has been said above. So also it appears to be inde- 
pendent of the intensity of the agent’s action. Fuchtbauer found the 
velocity of the § rays produced by canal rays to be independent of the 
intensity of the primary rays; Lenard found the same for ultra- 
violet light. ; 
In my own experiments on the a rays (Phil. Mag., March, 1907), 
I have-brought forward evidence to show that the amount of ioniza- 
tion produced in an atom is proportional to the volume of the atom 
approximately. Taking this, in conjunction with the rule that the 
ionization produced in a gas is nearly proportional to the inverse of 
the speed, we have the very simple, if approximate, law that the 
ionization produced by an a particle in any atom under any circum- 
stances is inversely proportional to the time spent inside the atom. 
This appears to point to the ionization as purely a trigger effect. Not 
that the a particle spends no energy in the atom; it is clear it must do 
so, since its speed is gradually reduced, but there is not a direct con- 
nection between the energy spent and the number of ions produced. 
But whatever energy the ionizing agent may spend, or in what- 
ever way it may spend it, it seems likely that the issue of the 8 particle 
is the result of some disruption in the atom, or subatom, which is the 
same for all atoms and under all circumstances. 
Jf we turn our attention now to all secondary radiation other than 
the 8 rays, it seems to be, in general, a rough reflection or scattering 
of the primary. Allen has shown that there is only a little less ve- 
locity in the secondary rays than in the primary £ rays, or in the ter- 
tiary than in the secondary. McClelland has measured the total ioni- 
zation produced by the secondary as compared with the primary 8 
radiation; and since he used a small ionization chamber with which 
he explored the whole space traversed by the secondary rays, which 
chamber the secondary rays would, as a rule, completely cross if they 
entered it, it may be taken that he really compared the number of 8 
particles in the secondary beam with the number of those in the pri- 
mary. ‘The numbers which he obtained varied from 15 per cent to 
50 per cent, according to the substance, which is the order of things 
we should expect if the secondary were simply scattered primary 
radiation. Again, the loss of velocity of the cathode particles, which 
is found to occur on scattering at a plate, presuming the secondary 
