Tonization produced in Gases by Réntgen Rays. 371 
In the former series of experiments the automatic regulating 
bulb was used, and as previously mentioned this bulb was 
very constant in the type of rays which it gave out; and the 
numbers given in Table VI. can be very fairly compared with 
one another for that particular type of rays. In the latter 
case, in which much harder rays were used, such strict 
constancy was not attainable, as is of course almost invariably 
the case when working with very hard rays. It is not 
possible to maintain a very “hard” bulb so constant in its 
radiation as a “soft”? one. The numbers in Table VII. 
cannot therefore be quite so strictly compared with one 
another as those in Table VI., but nevertheless they show 
the relative ionization in these gases for hard rays of approxi- 
mately the same type. The chief point which they illustrate, 
however, is the considerable difference in the relative values 
for the ionization in these gases for the two types, hard and 
soft rays. 
General Consideration of Results. 
The series of experiments which have been described in 
this paper show conclusively that the relative ionization pro- 
duced by Rontgen rays in different gases is not constant but 
depends very much upon the type of rays which are used as 
the ionizing agent. The change from hard to soft rays 
appears to affect different gases to quite a different extent. 
As far as these experiments go, the chief factor in producing 
this effect appears to be the state of the vacuum in the 
Rontgen-ray bulb which produced the rays. The pressure of 
the gas in the bulb may not be the sole cause of this difference, 
but it certainly is a very important factor in producing this 
effect, as 1s shown very conclusively by the results given in 
Tables II. to V. Other conditions of the Roéntgen-ray bulb, 
such as the sort of electrodes used in it, &., may also aid in 
producing a difference in the type of rays which affect 
different gases to a different extent. To such causes may be 
partly due also the differences in the type of rays which pro- 
duce the differences in the relative amount of ionization in 
air and hydrogen obtained by using different bulbs, as 
shown in Table I. Whatever may be the causes which 
produce rays of different types, it is quite evident from these 
experiments that the relative amount of ionization produced 
in any two gases by Rontgen rays is not a fixed ratio, but 
that the ratio is a function of the type of rays which pro- | 
duce the ionization. 
This variation in the relative ionization does not appear to 
depend in any definite manner upon the intensity of the 
radiation so long as the nature of the rays remains the same. 
