PHYSICS: D. L. WEBSTER 165 
1 
E = ki--\-t — p ^ xe 
0 
klz+z - P 1 xe '^dx 
or approximately 
72 
12^2 qjH- 
In a previous paper by the author^ it was shown that, neglecting absorp- 
tion in the target, the intensity per electron and per atom and per unit interval 
of frequency from an extremely thin target would be 
where b is the coefficient of the Thomson-Whiddington law in the form 
Fo^ — VJ^ = bx, and N is the number of atoms struck per unit length of the 
electrons' path. This equation is of course subject to some error due to ab- 
sorption in the target, and as one may readily prove, could be corrected by 
adding to i a term 
where a is the ratio of the distance travelled in the target by the emerging 
X-rays to the distance travelled by the cathode ray before it emits X-rays, 
and fjL is the linear absorption coefficient. This correction is important only 
at low frequencies. Neglecting it, we have 
with k, p and q all constant. It must be remembered that the data are 
very incomplete and this result is unreliable and is presented only for lack 
of anything better. But the true law must have something of the same 
general characteristics as this, and certain conclusions about the emitting 
mechanism can be drawn from that fact. 
First, let us assume that some form of quantum law governs the radiation 
of frequencies different from V/H as well as at that one. We are then prac- 
tically though not rigorously led to one of two alternatives. If the quantum 
law merely regulates the frequency being emitted at any instant in terms of the 
energy still available at that instant for radiation, so that the radiation by 
one electron is not monochromatic, then every electron radiating at all must 
radiate some energy at the highest possible frequency, V/H, and presumably 
give up all its energy to radiation. But this would make i(V, v) independent 
of V, and is therefore improbable. The more probable alternative is that the 
radiation by one electron is monochromatic, and the quantum law gives its 
