50 
PEOFESSOR E. RUTHERFORD AXD 5IR. E. K. ^^IcCLUNG 
investigation has shown that for the same range the intensity of the ionization is also 
approximately proportional to the pressure. This shows that for the pressures 
examined the ionic energy is independent of the pressure. The results on the 
variation of absorption with pressure for uranium'^ and thorium t radiation also point 
to the same conclusion. 
In order to fully establish such a general law that the energy to produce an ion is 
independent of the gas and its pressure, a large number of careful experiments will 
be required. The results so far obtained can only be considered to show that such a 
law is approximately true. It is intended to continue these investigations on ionic 
energy for other gases besides air and carbonic acid. 
Deductions from the Results. 
If ions of the same kind are joroduced in a gas by different agencies, it is 
probable that the same amount of energy has been absorbed to jjroduce the ions in 
the different cases. The only test we have at present for equality is to compare the 
velocity of the ions in the gas for a potential gradient of 1 volt per centim. 
J. J. Thomson has .shown that the charge on an ion produced by Ptontgen rays is 
probably the same for the gases hydrogen, air, oxygen, and carbonic acid, and 
Townsend| that it is equal to the charge on a hydrogen ion in the electrolysis of 
water. The velocity of the ions in a given electric field depends upon the ratio 
ej-ni of the charge to the mass of the ion, and thus if the velocities of ions 
produced in the same gas by different agencies are the same, the masses must be 
the same, since the charges are ec|ual. 
It has recently § l:)een shown that the ions in the “electric wind” travel in air 
with the same velocity as the ions produced l^y rays. Tlie energy used up in 
producing the ions can thus ])e immediately calculated. 
Let i — the current through the gas due to the electric discharge from a wire 
or point. 
Energy absorbed in producing ions = n W — — W, 
where n is the number of ions produced per second and e the charge. 
Therefore, neglecting recombination of the ions, 
- W 
Energy recpiired to produce ions _ e _ ^ ^ 
Total loss of energy Xi e 
where V is the potential of the discharging wire. 
E. Rutherfoiid, ‘Phil. Mag.,’ January, 1899. 
t R. B. Oavexs, ‘Phil. Mag.,’ October, 1899. 
I ‘Phil. Trans.,’ A, 1899. 
§ Chattock, ‘Phil. Mag.,’ October, 1899. 
