732 Prof. Bragg and Mr. Kleeman on the 
whilst P represents the rays from the last induced activity. 
Rutherford has shown that the rays from induced activities are 
more penetrating than those from the radium itself. Moreover, 
the rays that are represented by P go twice as far as those 
repr esented by Q or R, and do twice as much ionization. In 
the figure given on p. 262 of Rutherford’s book, it is seen that 
Fig, 4.—Ionization curve of dish five days after being raised to a red heat. 
7 
DISTANCE /N CM. FROM RADIUM TO IONISATION CHAMBER. 
££ 
I 
(@) ay 1-0 5 
LEAK OF ELECTROMETER IN MM. DIVISIONS OF SCALE PEA SECOND.-, 
the area of the curve representing the total activity of the 
second induced activity is much greater than that belonging 
to the first. In fig. 5, I. represents the curve of a dish thirty 
hours before heating : it must have moved somewhat to 
the right before the operation. Curve H. shows the result 
of heating; readings were taken downwards, and occupied 
twenty minutes. “Curve III. was obtained on going up 
again, and the decay of P is clearly shown. 
“It is not so easy to separate ( from R, and to find which 
is emanation and which the first induced change. Hither 
the red heat which drives off one drives off the other also, 
or the induced activity dies away so fast when the emanation 
is removed that it is hard to catch it before it is gone. We 
cannot with our instruments take one reading in less than 
thirty seconds; and this is too slow. We have, however, 
