74 ROYAL SOCIETY OF CANADA 
Very often the movement of the needle was too rapid to observe by 
means of the eye, so that when this was the case, a condenser was 
connected in parallel with the electrometer cutting down the current 
to any desired ratio. Several readings were always taken at a time 
and they were always quite consistent. The electrometer and all 
connecting wires were surrounded by metal screens connected to 
earth, preventing any stray electrical effects from reaching the electro- 
meter. All the woodwork, ete., in the neighbourhood of the electro- 
meter was covered with metal and earthed. 
DECAY OF RADIOACTIVITY. 
Many experiments were made to determine the rate of decay of 
excited radioactivity. The charged wire was supended in different 
places, such as in closed rooms and in the air outside the building. 










Fig. 2 shows two such curves plotted. I. A copper wire charged 
for 210 mins. at a P. D. of — 25,000 volts inside the closed room. 
II. A copper wire charged for 270 mins. at a P. D. of — 24,000 volts, 
outside in the open air. An examination of these curves shows that 
they fall to one-half their value in about 50 mins., following very 
closely a geometrical progression, as can be seen by the following 
results: 
CURVE I. 
Falls to 4 value in about 52 mins. 
66 + LA2 “ec 96 «6 
“cc 4 «6 oe 176 « 
CURVE II. 
Falls to 4 value in about 48 mins. 
“ce t «6 “ce 97 (41 
“oe 2 [212 “ce 188 “cc 
