TRAVERSED BY CATHODE RAYS. 
71 
the coefficients of ionization for a series of gases are fully determined when the 
coefficients of absorption for these same gases are known. 
The existence of this general relation between absorption and ionization for botli 
cathode and Rontgen rays is especially interesting when we remember that the two 
radiations are so very different in many respects. 
In the one case, according to the generally-accepted view, the rays consist of 
small charged particles of matter moving with high velocities in space, while in the 
other they are supposed to consist of electromagnetic impulses propagated in the 
ether. With the one the dissociation is in all probability brought about by a series of 
impacts between the moving particles and the molecules of the gas; with the other 
it seems to be due to the direct action of the intense electric field forming the impulse. 
Again, while the absorption of cathode rays depends only upon the density of the 
medium traversed, the absorption of Rontgen rays, according to Rutherford’s 
results, does not seem to depend to any great extent upon the molecular weight of 
the gas. But while all these differences exist in the two radiations, with both of 
them it holds good that the same number of ions are always produced in a gas when 
the same amount of rays traversing it are absorbed. 
11. Comparison of Ionizations produced by Cathode and by Rontgen Rays. 
The method just described gives definite and conclusive information regarding the 
ionizations produced by cathode rays in gases of the same density; but where the 
gases are of different densities, it cannot be satisfactorily applied. As stated in 
Section IX., the rays, after entering the ionizing chamber, must travel some distance 
before reaching that part of the field from which the current is drawn. On this 
account, though rays entering the chamber may originally be of the same strength, 
still their effective intensities become at ordinary pressures cpiite different, when the 
gases traversed are not of the same density. 
Also as it is impossible to define exactly the disposition of the electric field within 
the chamber, these effective intensities cannot be calculated with auy degree of 
accuracy. 
A difficulty arises, too, from the dispersion of the rays. As shown by Lenard, 
they issue from the window in a pencil whose form is greatly influenced by the 
density of the gas traversed. At very low pressures they pass through the 
aluminium window practically without deviation, but as the pressure increases, they 
spread out until finally they issue in all directions. 
The conclusion arrived at in the last section, however, suggests a means of calcu¬ 
lating the ionization which would be produced by rays of constant intensity in 
different gases at the same pressure. 
Lenard,* who investigated the absorption powers of a number of gases at different 
* ‘ Wiecl. Ann.,’ vol. 56, p. 258. 
