48 
PROFESSOK E. RUTEIPRiFORI) AXD MR. R. K. McCLUXG 
the variation of the penetrating power of the rays as the bulb varies. The value 
of X determined for tlie rays, under different conditions as regards the frequency of 
the Wehnelt interrupter, was found to be apj)roximately the same, after the l)ulb 
had l)een in constant use for several months. It is probable that the type of 
rays does not on an average vary much from day to day, but the greatest source 
of error is probaljly due to the assumption that tiie rays are homogeneous in 
character. Rontgen and others have shown, from experiments oii the absorption of 
successive thicknesses of metal, that rays ai'e not simple in character, but contain 
rays of widely different order of penetrating power, so that the value of X is the 
mean value for the different ty})es of rays. 
The value of W also depends upon the value of e, tlie charge on an ion, and if 
future investigations should assign a different value to e, the value of W would be 
altered in a like ratio. 
Energy required to 'produce an. Ion in other (jases. 
When the energy required to produce an ion in one gas is known, the energy 
re(pnred to jJroduce an ion in another gas can be detei'inined from the ratio of the 
absorptions of tlie rays and the intensity of ionization in the gases. 
Let ;q and n.^ be the number of ions produced per cub. centim. in two gases. 
Let X| and X^ be the coefficients of absorption. 
Let and l)e the energies re(piired to produce ions in the two gases. 
Let q and L be the maximum currents through the gases. 
Then for the same intensity of rays, 
AJ _ 
— ryy-’since h — assuming 
charges on the ions are equal. 
_A,2 q 
W “ ’ b ' 
Tlie ratios X.dX.^ and q/L can be readily determined, and if W^ is known, then W^ 
can be calculated wdthout recourse to experiments on tlie heating effect of the rays 
in each case. 
Idle value of X^, tlie lutio of the absorjition coefficient of carbonic acid gas to 
that of air, was found to be 1’59 for the rays employed. The ratio q/q Hie 
current in air and carbonic acid gas for a potential difference of 300 volts was found 
to be 1'43. 
Therefore the energy required to jn'oduce an ion in carbon dioxide 
= -|-|^XXq = fllWi = 2-11 X 10-^Wrg. 
absorption of energy in gas.^ 
absorption of energy in gas^ 
Idierefore 
