﻿Substituting the value 



\ = 



the a. particles expelled from Radium and Actinium. 357 



d 



I 2 ' 



MM 



In most o£ the experiments to be described later, 



Z 3 = 3*94 cms., ^ = 3*77 cms., d = '21 mm. 



Consequently, D=l*09 mm. 



From the data given below it will be seen that the 

 formula (2) applies for all voltages greater than about 300, 

 while the formula (1) applies for all values smaller than 

 this. 



Results of Experiments. 



The electrostatic deflexion of the a rays from radium C 

 was first determined for different voltages between the plates. 

 The rays from the active wire passed through a mica plate in 

 the base of the vessel, equivalent in stopping power to about 

 3*5 cms. of air. The extreme distance D between the outside 

 edges of the photographic impressions obtained on the plate 

 by reversal of the electric field was measured by the lantern 

 method described in a previous paper*. 



In most of the experiments, the value l z of the distance of 

 the photographic plate above the parallel plates was 3'9-f cms. 

 In one experiment this distance was 10*00 cms. 



Z i = 3*77 cms., Z 2 =4*165 cms., d — 0*210 mm. 



2 



The values of obtained for different voltages and 



distances of the photographic plate are tabulated below. 



Volts between 

 plates. 



h- 



D. 



rnit 1 

 e 



171 



394 cms. 



- 857 muis. 



51 X10 14 



255 



)> }> 



0995 „ 



4-9 X10 14 



340 



„ ,, 



1-136 „ 



4-93 xlO 14 



497 



,, „ 



1-341) „ 



4-79 x 10 14 



508-6 



10-00 .., 



3-10 „ 



4-87 XlO 14 



Each of the values of D given above is the mean of a large 

 number of separate measurements which agreed closely among 



* Rutherford, Phil. Mag. August 1906. 



