94 Lifect of Temperature on Lonization by Réntgen Rays. 
TasLe [V.—Hydrogen. 


Ps ee ee | Ionization as represented | Temperature of 
by Scale-Divisions for | = is ee aie 
’ : | by Seale-Divisions for Ain 
Dae og tate ae | Standard Apparatus Cylinder AB 
filled with H.,. | PP a tlh da 

89 | 299 226° C. (approx.) 

96 | 295 | 187° ogee 
88 | 302 | 148° i 
78:9 304 | 112° . 
79:9 295 78° Z 
66:7 | 284 1 14° is 



Although there is considerable variation in the above 
numbers, still I think this want of constancy can be accounted 
for chiefly by the leakage in the vessel. However, from all the 
results obtained, I think we may safely conclude that hydrogen 
follows the same law for the effect of temperature on the 
ionization as has been established for air and carbon dioxide. 
INscussion of Results. 
_ The experiments described in this paper have proved con- 
clusively that ina given volume of gas, kept at a constant 
density, the amount of ionization produced by Rontgen rays 
of a given intensity is independent of the temperature of 
the gas. Prof. Perrin, in the paper to which reference has 
already been made at the beginning of this paper, described 
some experiments which he made on this same question. The 
results which he obtained are, however, not in agreement 
with those which I have just given in this paper. The method 
which he employed was a differential one. He made the rays 
to pass simultaneously between two sets of parallel plates. 
He then balanced the effect produced on one set of electrodes 
against that produced on the other set, so that the resultant 
effect produced on the electrometer was zero. This balance 
was adjusted at a certain temperature, and then the tempera- 
ture of the gas in the vessel containing one set of plates was 
varied and the balance then tested. For the range of tem- 
perature from —12° to 148°C. he found no appreciable 
alteration in the balance. He concludes therefore that, since 
no change in the balance occurred and the density of the air 
varied inversely as the absolute temperature, the total ioniza- 
tion would be proportional to the absolute temperature in air 
maintained at a constant density. JI cannot account with 
