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LXXIV. On the Ionization Curves of Radium. By W. H. 
Braae, J.A., Professor of Mathematics and Physics in the 
University of Adelaide, and R, KLEEMAN*. 
a paper “On the Absorption of a Rays, and on the 
Classification of the a Rays of Radium,” contributed by 
one of us to this Magazine f, a description was given of a 
method of obtaining curves which represented the ionizing 
effects of a2 rays at various distances from their source. It 
was shown, aiso, that the general form of the curves supported 
the hypothesis that the e particle passes, in its flight, through 
the matter which it traverses, without any appreciable de- 
viation, and only loses its extraordinary velocity when it has 
expended on ionization the ionizing powers which it possesses 
by virtue of that velocity. Such a fast moving atom must 
become positive, as the « atom is known to do, and as perhaps 
the emanation atom does when it recoils after expelling an 
a particle. In an experiment on the ionization curve of 
de-emanated radium, 5 mmg. of radium bromide were dis- 
solved in a little water in a test-tube. Air was bubbled 
through the solution for many hours. The liquid was then 
evaporated, and the bottom of the tube on which the radium 
was deposited was cut off, and placed in the testing apparatus. 
Although the fragment of glass was of very irregular form, 
and the curve obtained was distorted by the want of regu- 
larity, yet after a few days an effect appeared which could be 
ascribed with certainty to the fact that the radium layer was 
thin, and that 2 rays from even the lowest stratum of it were 
effective in the ionization chamber. The curve, in fact, had 
a vertical portion: the interpretation of this being that for 
some distance of approach of the radium towards the chamber 
there was no increase in the ionization. A few words of 
explanation will make this clear. 
In the paper referred to, it was shown that when a shallow 
ionization chamber is gradually brought closer to a source of 
avays of uniform initial velocity, the rays being limited by 
stops to a narrow cone, and the chamber being wide enough 
to take in the whole cone at all distances, then the ionization 
increases in proportion to the amount of approach. For as 
the distance is diminished the curve includes a rays from 
deeper and deeper strata in the radium. Thus, if ordinates 
represent distances from radium to chamber, and abscissee the 
leaks shown by a quadrant-electrometer in consequence of 
* Communicated by the Authors. 
t+ Supra, pp. 719-725 
