Lonization produced in Grases by Rontgen Rays. 83 
burner placed underneath the outside cylinder, and which 
ran almost the whole length of the iron cylinder. The air in 
the brass cylinder was thus surrounded by a jacket of heated 
air, and by regulating the supply of gas to the burner the 
Fig. 1. 
KWAN 
EARTH 
SRW 
LARTH 

Kwon 
RSs 
LARTH 
temperature of the air in the cylinder BC could be kept 
fairly constant for a considerable time. The temperature of 
the air was measured by the two mercury thermometers T 
and T’ shown in the diagram, and the mean of the temperatures 
indicated by these thermometers was taken as the average 
temperature of the air under investigation. 
The electrode E’ was connected in parallel with a con- 
denser to one pair of quadrants of an electrometer, while 
the other pair was to earth. The electrometer used through- 
out the experiments was one of the Dolezalek type which 
gave about 2000 scale-divisions for a difference of potential 
G 2 
