1438 
warmed air is directed upon the amber, which at the same time 
dries the lower part of the vacuum glass. 
Finally, the cooling of the parts of the connection of the main 
electrode /, with the electrometer must be prevented. To attain this 
a current of dry and slightly warmed air is also directed upon 
the amber stopper between the stem /,, and the protecting ring Z, 
at the bottom of the main ionisation chamber. 
The cold currents of air, which come down from the tubes that 
lead off the gases, are diverted from the apparatus by suitable 
screens, and large currents of air in the room are avoided as far 
as possible, so as to prevent the ionised air around the contacts 
from being displaced ; these contacts were further protected by various 
lead protecting mantles (in the figure diagrammatically represented), 
by tin foil, ete. The influence of the warm currents of air already 
mentioned was tested at the temperature of the room: they did not 
cause any electrostatic phenomena. 
Preparatory Experiments. 
The experimental method was first studied in Paris, using liquid 
air as cooling bath. 
The current in the main ionisation chamber was procured by 
using a tube with about 0.1 er. of radium chloride. In the com- 
pensation chamber a tube with about 25 mgr. of radium chloride 
was used. 
In the first experiments the first tube was contained in an aluminium 
tube with walls of 0.3 mm. thickness; the central tube D, in the 
chamber D, was also of aluminium, with walls of 0.5 mm. thickness. 
The rays, before penetrating into the ionisation chamber, passed 
through a layer of aluminium of about 0.8 mm. and moreover a 
glass layer about 2.5 mm. (wall of the radium tube and both walls 
of the vacuum glass). 
During the cooling a diminution of the current in the main chamber 
could be observed. It was not very regular, and amounted to. about 
2°/,, it was perceptible immediately after the liquid air was poured 
into the copper vessel, and reached its maximum in about half an hour. 
When, however, the liquid air was quickly taken out of the 
vessel, and tke temperature of the radium tube was followed with a 
thermoelement, it could be observed that while the temperature of 
the radium tube was still constant, the strength of current already 
began to rise, and reached about its original value, by the time the 
whole apparatus had returned to ordinary temperature. From this it 
was evident that the decrease of strength of current which we observed 
