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BELL SYSTEM TECHNICAL JOURNAL 



the end-point of the cur^-e is located, but the entire shape is considered, 

 the conditions of the experiment being so fixed as to make this shape 

 significant. The experiments are, in fact, made upon the distribution- 

 in-range of the ejected protons. Strata of gas or films of solid are 

 interposed in the path of these particles, and the number which get 

 through various thicknesses of these obstructions is carefully measured. 

 The "air-equivalent" of the obstructions is separately measured, and 

 so one is able to plot a curve of which the abscissa R is range in air at 

 conventional pressure and temperature (760 mm. Hg and 0° C, in the 

 figures which I show next) while the ordinate is the number of corpus- 

 cles having ranges greater than R. 



This newest and sensational work was done by Pose at Halle. I 

 show in Fig. 5 his sketch of his apparatus. In the evacuated chamber 



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Fig. 5 — Pose's apparatus for detecting transmutation of metals by an ionization 



method. 



above, the button under the letter P carries the radioactive source — a 

 layer of polonium, a substance of which the alpha-rays have a range 

 smaller than those of which I have been speaking, 3.72 cm. only in air 



