Lonization produced in Gases by Réntgen Rays. 363 
by opening the keys M and N, which worked by means of 
strings from a distance, and the electrode K was allowed to 
charge up for a given length of time. There was also a 
capacity in parallel with K. Since K was quite insulated 
from the electrometer it was, therefore, first observed whether 
the balance between a and a’ remained steady, and then at 
the end of a given time the rays were shut off and the key N 
was closed and the charge in the electrode K was measured. 
The balance and the intensity of the ionization were thus 
tested simultaneously. | 
The two cylinders BB’ and CC’ were filled with air at 
atmospheric pressure and a balance established, and the 
strength of the ionization tested in the standard apparatus, 
One of the cylinders was then exhausted and filled with 
hydrogen at atmospheric pressure. The other cylinder con- 
taining the air was then partially exhausted until the ioniza- 
tion in it just balanced the ionization in the hydrogen. This 
balance and the intensity of the ionization were again 
tested. | 
Several experiments were made using the automatic re- 
gulating bulb, and extremely constant results were obtained: 
Although these results, giving the ratio of the ionization in 
hydrogen to that in air, agreed so extremely well among 
themselves, yet this ratio differed very considerably from any 
of the numbers obtained by the previous observers. This 
fact, therefore, suggested the possibility that if a different 
X-ray bulb were used the ratio might be altered. Several 
other bulbs were consequently tried and quite different results 
obtained with them. None of these bulbs were automatic 
regulating ones, but were of the ordinary form of focus-tubes. 
There was no means of keeping the pressure in them quite 
constant, and therefore the rays given out were liable to vary. 
Not only did the different bulbs give different results, but in 
some instances the results obtained at different times from the 
same bulb varied among themselves. The results obtained from 
the various bulbs on different occasions are given in Table I. 
All the determinations and the dates on which the experiments 
were made are inserted to show how constant the results 
remained in the case of the bulb which was regulated auto- 
matically, although the experiments extended over a con- 
siderable time, while in the case of bulb No. 2, which was not 
so regulated, the results varied from time to time. Bulb 
No. 1 was the automatic regulating one, while the others 
were all nonautomatic. 
