382 Miss H. Brooks on the Decay of the Excited 
gives rise to the production of @ rays. In fig. 3 are given 
curves for the @ rays for different times of exposure. The 
-curyes for all times of exposure have a common rate of decay 
after a certain time; the first part of the curves here given 
indicates the rise in the radiation for the different times of 
exposure plotted to the scale of the curve of decay for a long 
exposure. 
The y rays were measured in a similar manner: a screen of 
lead was interposed between the radioactive body and the 
electroscope to cut off the aand 8 rays. ‘They rays evidently 
accompany the production of @ rays, as their rate of decay 
was the same in all cases examined. Fig. 4 shows the decay 
Fig. 4.—Excited activity of Radium for different times of exposure 
measured by the y rays. 
Intensity Of Fa ation 
0 10 20 30 40 50 60 70 80 90 
7/f7e (7 snii7meles. 
of the y rays for a long and a short exposure, both plotted to 
the scale of the long exposure. 
Eexcated Activity from Actinium. 
Actinium, like radium and thorium, continuously emits a 
radioactive emanation which has the power to excite a tem- 
porary radioactivity on a negatively charged conductor ex- 
posed to it. The rate of decay of this excited activity has 
been given in a recent paper by Debierne* as a gradual 
' * Comptes Rendus, no. 138, p. 411 (1904). 
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