10 M. Levin — Absorption of the a-Raysfrom Polonium. 



meeting of the American Physical Society in December, 1905. 

 A short abstract of his results appeared in the Physical Beview, 

 but no numbers were given. 



Measurements by the Electrical Method. 



The apparatus used* for these experiments was quite similar 

 to that used by Bragg and Kleeman. A* metal box contained 

 the ionization chamber and the polonium rod. The chamber 

 consisted of two insulated plates about *50 cm apart, the upper 

 plate being connected with the electrometer and the lower 



; ; 



*<? ro. 



Ionization. 



To 



plate of wire gauze with the battery. The polonium rod was 

 placed in a little groove made in a lead block and was covered 

 with a lead plate about -6 cm thick having a circular hole of '4: cm 

 diameter passing vertically through it. The lead block was 

 placed inside the vessel on an upright support, which could be 

 moved vertically. The cone of rays issuing from the opening 

 in the lead plate was sufficiently narrow so that its cross-section 

 never covered the whole surface of the ionization chamber. 

 The saturation-current produced in the ionization chamber was 

 measured for different distances between the polonium rod and 

 the wire gauze. 



The ionization of the rays in air at different distances from 

 the source was first investigated. The results are shown in 

 figure 1, where the ordinates represent the distance from the 

 upper surface of the rod to the gauze in centimeters, the 

 abscissae the ionization measured in arbitrary units. 



* I am indebted to Dr. Hahn for his kindness in allowing me to use the 

 experimental arrangement which he had previously employed in his deter- 

 minations of the range of the a-rays from the products of thorium and 

 actinium. 



