on Ionization produced by Hot Platinum in Gases. 401 
month. In that paper it was shown that the positive leak 
from hot platinum in vacuo fell off in a definite manner 
with the time, so that a platinum wire which had been heated 
long enough at a low pressure lost the power of producing 
positive ionization. It was also shown that such a wire 
could have its leaking power restored in several different 
ways. It is with one of these, viz. exposure to a luminous 
discharge, that the present paper deals. 
The sequel will be made clearer if we consider for a 
moment what happens when a platinum wire, which has been 
strongly heated so that it exhibits no detectable leak at a 
temperature of say, 650° C., is placed for a time near the 
cathode in a vacuum-tube whilst a luminous discharge passes. 
On heating the wire again, it will be found to discharge 
positive electricity at temperatures far below 650° C., although 
it is still incapable of discharging negative electritication. 
If such an exposed wire be maintained at a constant tempe- 
rature, it will commence by discharging electricity at a rate 
which is greater the higher the temperature. Thus at a low 
temperature we have a small current for a long time, and at 
a high temperature a big current for a short time. On the 
view, suggested in the previous paper, that the ionization is 
due to the decomposition by heat of some foreign substance 
imparted to the platinum, we might expect that the integral 
of the current with respect to the time, z. e. the total quantity 
of electricity discharged, would be independent of the tem- 
perature. This question has not yet been tested directly, 
but experiments which it is hoped will decide it are at present 
in progress. , 
‘The alteration in the wire by virtue of which it possesses 
the power of discharging positive electricity at a lower tem- 
perature than heretofore, the author proposes to call the 
imparted emissibility; this appears to be preferable to the 
term “induced activity” employed in the former paper, since 
it avoids confusion with radioactivity. As a means of investi- 
gating these effects the measurement of the total quantity of 
electricity set free when the wire is maintained at any tem- 
perature below that at which the normal leak makes itself 
felt, has been employed; in comparative experiments this 
temperature was always made the same. Whether the 
quantity concerned is different for different temperatures is, 
as has been stated, at present under investigation. In the 
sequel the quantity of electricity emitted under the above 
conditions, which measures the imparted emissibility, has 
also been called the imparted emissibility; since the two 
uses of the term are not likely to cause confusion, and it is 
