on Ionization produced by Hot Platinum in Gases. 407 
constant and equal to ‘308 milliampere, and allowed to pass 
for 120 seconds. The imparted emissibility was found to 
increase from 8&5 to 58 arbitrary divisions as the pressure 
fell from ‘81 to °33 millimetre. Some experiments were 
also made at a pressure of ‘025 mm., using the discharge 
from an induction-coil; it was found that for the same 
current-strength and duration of the discharge, the imparted 
emissibility at this pressure was about 50 times as great as at 
a pressure of -£ mm. 
Experiments were also made to see if the emission of 
positive electricity by a wire which had been exposed to the 
discharge was accompanied by the evolution of a measurable 
quantity of gas. The result showed that if any gas were 
given off, its “volume at atmospheric pressure must be less 
than 1/100 that ef the testing wire. This result does not 
prove that the effect is not due to occluded gas, for calcula- 
tion shows that if each molecule of gas produced an ion, the 
volume required would only be one ten-thousandth of the 
above amount. 
The effect of exposure to a luminous discharge on the per- 
manent negative leak from a platinum wire was also tried. 
It was found that the discharge reduced the leak temporarily 
to a small value, from which it gradually recovered. At the 
temperatures at which the experiments were made, it was 
found that the wire took about fifteen minutes for the nega- 
tive leak to reach its normal value again. The reduction 
appeared to be considerably greater than that which would 
correspond to the positive ions set free. 
In all the experiments on ihe imparted emissibility the 
testing wire was of platinum. Similar effects were obtained, 
however, with cathodes of platinum, aluminium, and carbon. 
The emissibility i in a tube which consisted only of platinum 
and glass did not appear to be materially reduced by cleaning 
the tube with hot nitric acid and distilled water. 
Experiments were next made to see at what temperature 
the emission of positive electricity from an exposed wire 
commenced, and how the rate of emission varied with the 
temperature. It was found that at low temperatures, when 
the leak first began te be perceptible, it varied with the tem- 
perature according to the formula Ae~*®, In this respect 
the imparted effect only furnishes another example of the 
general law, that in all cases of steady ionization by het 
bodies the number of ions produced per second is given by a 
formula of the type A@?e—*%, where A and 6 are constants 
and » is a numeric which does not differ sufficiently from 
zero to make the variation with 0 of 6? comparable with that 
of the exponential term. When the reaction which produces 
