142 Mr. S. J. Allan on the 
and the cylinder was arranged a guard-ring, to prevent any 
Jeak around the ends of the electrodes. The rate of move- 
ment of the electrometer-needle was taken as a measure of the 
amount of excited activity present. The wires were always 
tested five minutes after removal from the attic. 
The results obtained from these experiments are given in 
ihe following Table, the second column giving the amount of 
excited activity on the wire five minutes after it was taken 
down. 
TaBLe I. 
Time of exposure. Excited activity produced. 
22 minutes. 6 divisions per sec. 
60 3: 12 29 9 
90 29 16 99 ” 
10a ee Sonn one 
138 ss 24 my : 
200 A 26 i 4 
The results are shown graphically in fig. 1 (Pl. XIV.). 
From an examination of these results it will be seen that 
the excited activity increases with time according to the equa- - 
tion given above, rising to half value in about 60 minutes. 
It has been shown that the excited activity on a charged 
wire decays to half value in 45 to 48 minutes. The results 
are thus only approximately in agreement with theory, since 
it is difficult under the experimental conditions to obtain more 
than rough results. 
Rates of Decay under various Conditions. 
In the previous paper it was shown that the excited acti- 
vity on a charged copper wire always had the same rate of 
decay, wherever and whenever produced. It was, however, 
deemed advisable to examine the rate of decay of the excited 
activity produced under as many different conditions as 
possible. 
lron and lead wires were tried and each gave the same rate 
ot decay as the copper wire. Hxperiments were then made 
to see if by transferring the excited activity from the copper 
wire to such substances as leather and felt, by means of 
ammonia, any difference could be observed in the rate of 
decay. For this purpose about 150 feet of copper wire was 
suspended in the attic and kept charged for about three hours 
a constant negative potential of 20,000 volts. A piece of 
leather, about 7 cms. square, moistened with ammonia, was 
then rubbed over the wire, and by taking care to rub a fresh 

