Ci ss 
ia 
60 IONIZATION THEORY OF GASES [CH. 
An interesting result follows from the rapid absorption of 
radiation by the gas. If the current is observed between two 
fixed parallel plates, distant d, and d, respectively from a large 
plane surface of active matter, the current at first increases with 
diminution of pressure, passes through a maximum value, and 
then diminishes. In such an experimental case the lower plate 
through which the radiations pass is made either of open gauze or 
of thin metal foil to allow the radiation to pass through readily. 





















Pressure in mms. 
150 300 450 600 750 
Fig. 8. 
The saturation current 7 is obviously proportional to 
ry Ad 4 I, Ned Ma 
pl,e?™4, i.e. to i, (e-PAd, — g—PA.d2), 
qd, 
This is a function of the pressure, and is a maximum when 
log e d, = — pr, (d, — d,). 
d, 
