980 Prof. 0. W. Richardson on the Positive 



on the strip. The latter was then heated until the salt 

 melted. In this way, a uniform layer of the salt was obtained 

 over the whole of the front surface of the strip. The 

 apparatus was again set up and exhausted. The distribution 

 of the positive ionization on the opposite planes was now 

 determined after the salt had been heated for different lengths 

 of time. Throughout this investigation a difference of 

 potential of 200 volts was maintained between the plane 

 containing the strip and that containing the slit, the strip 

 being positive. In all the experiments with lithium sulphate 

 the transverse magnetic field was of strength 4700 lines 

 per cm., and measurements were made with it first in one 

 direction and then in the other. Jn some cases experiments 

 wore also made in the absence of a magnetic field. The 

 distance \ between the plates near the slit and the back of 

 the strip was measured, by focussing with a microscope 

 furnished with a micrometer arrangement for vertical dis- 

 placement-, from time to time during the course of the 

 experiments. The apparatus was continuously exhausted by 

 means of a Gaede pump, and the pressure recorded on the 

 McLeod gauge was kepi below "001 mm. In some of the 

 experiments il was a- low as 10~ fi mm. Provided the 

 pressure i^ less than -01 mm., its actual value does not seem 

 to influence the results. 



The results of the experiments can best be exhibited by 

 means of curves shoeing the fraction of the total number of 

 ions received by the plates which puss through the slit for 

 different positions of the latter. The rationale of this is 

 fully explained in the first of the papers already referred to *. 

 The units used are arbitrary since a capacity of *001 micro- 

 farad was always placed in parallel with the plates, whereas 

 there was no capacity except that of the electrometer and its 

 connexions attached to the slit electrode ; and the capacity 

 of the electrometer and its connexions was not determined. 

 It was, however, the same in all the experiments. 



The results of the experiments on the ionization from 

 platinum alone are shown in fig. 1 (PL XX.). These represent 

 two successive series of measurements with the magnetic field 

 in each direction. The points for the first series are shown 

 thus : 0, and for the second series thus : x . Although the 

 curves are not quite coincident, the displacement of the 

 maximum which gives the values of e/m and m is practically 

 identical for both sets. At the beginning of this experiment, 

 two measurements of the value of z gave *480 and *478 cm. 



* Phil. Mag. [6] vol. xvi. p. 740 (1908). 



