OF GASES UNDER THE BECQUEREL RAYS. 
511 
to rise, in order that a suitable reading of the rate of charge miglit be obtained, never 
exceeded this value. Now a slight leakage through h is of no importance, its only 
effect being to take a small current from the battery. On the other hand, a failure 
of the insulation of the stopper I would vitiate the measurements. But the danger of 
such a failure is but small, because of the smallness of the E.M.F. to wliich this 
insulation is exposed. If a simple ebonite stopper were used to carry the electrode, 
these more complicated arrangements being dispensed with, it would be essential that 
its insulation should be perfect even when exposed to tlie whole 200 volts. 
Fig. 1. 
^$\\\\\\\\\\\\\\\\\\\\\\\\\\^^ 
InsuLabeol eLecbromeber 
quadrAnbQ. 
'0 
The brass vessel was screwed down to a l)lock of lead, d, l:)y suitable thumbscrews. 
A circular cavity, c, was turned in this block, and served to contain the radio-active 
material. 
At p a side tube was soldered in, through which the apparatus could be exhausted 
and gas admitted. 
For investigating the easily absorbable radiation, a slightly different arrangement 
was employed. Instead of the thin copper bottom soldered on, a thick circular brass 
plate was used. On this was laid a lead tray containing the radio-active body ; the 
brass cover, in this case provided with a flange round the bottom edge, was then 
cemented on with the soft cement known as Puout’s Elastic Glue. 
Fig. 2 will make the arrangement clear. The vessel inside was connected to a 
water-pump, which would exhaust to a pressure of 15 millims., and to a manometer. 
