Ionization Curves of Radium. 729 
metallic connexion through the walls of the leaden cover D 
with the electrometer. A and D were insulated from an 
earthed brass ring F' on which they rested, and F was insulated 
from the lead plate. No leakage from the high-potential plate 
could therefore reach the electrometer. The chamber was 
sometimes flat, sometimes dome-shaped, as will be explained 
later. A platform supporting the dish and the tubes was 
placed below, and could be raised to any desired height. The 
dishes were about 2°4 cms. in diameter, and the tubes 1°5 to 
Zcms. in height. Except in one case specially mentioned, 
the dimensions were so proportioned that the cones, at all 
distances, fell completely within the chamber. The ionization 
chamber was usually about 3 mms. deep : in curves shown in 
any one of the figures given below, it was the same for all the 
curves of one figure. 
Fig. 2.—Ionization curve of dish prepared seven days before. 
N 
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nn 
ie eee a ee 
ae 
See 
— 
no 
ase 
DISTANCE 1/N CM. FROM RADIUM IN DISH TO LONISATION CHAMBER . 
aN £ 
ee See) 
-4L je -8 
LEAK OF ELECTROMETER IN Mm. DIVISIOWS 
_ OF SCALE PER SECOND. 
In fig. 2 is shown a curve obtained by the use of a dish 
which had been prepared seven days previously from de- 
emanated radium. <A set of seven tubes was used each 4 mms. 
