296 Danysz and Duane — Electric Charges of a- and fi-Rays. 



is roughly horizontal. The absorbing power of the glass cover- 

 ing each of the bubbles of emanation used in the experiments 

 was estimated by measuring the length of path of the a-rays in 

 the air after they had emerged from the spheres. These 

 experiments indicated that the glass in its thinnest place 

 absorbed the rays about as one centimeter of air would. It is 

 possible that the glass was not everywhere as thin as this, but 



Fig. 1. 



experiments described below proved that all the a-particles pro- 

 jected vertically upward emerged from the spheres. 



To produce a well-defined beam containing a known fraction 

 of the a-rays, the sphere was supported at A (fig. 1) inside a 

 metal cylinder B with thick walls. The distance from the 

 bubble of emanation to the top of the cylinder was 4*055 cm , and 

 the top contained a circular hole l-025 cm in diameter, so that 

 the ratio of the a-rays passing out through the hole to the total 

 number of a-rays supposed distributed uniformly in all direc- 

 tions around the source was '00400. 



In order to separate the charges of the a- and /3-rays from 

 each other a diaphragm D with a circular hole '602 cm in diameter 

 was fastened in the cylinder at a distance of 2*99 cra from the 

 top, and the apparatus was placed between the poles P of a 

 large electromagnet, the lines of force of the field being hori- 



