﻿1040 Prof. Townsend and Mr. Bailey on the 



If the ratio H = fi 2 '(ni -f-w 2 4 n%) be determined experi- 

 mentally when the stream is moving under an electric 

 force Z, the value of-Z/k corresponding to R is given by the 

 curves (fig. 3), and the factor k is thus found. The velocity 

 of agitation u of the electrons is then given by the formula 

 m=1'15x10 7 X \ k. None of the experiments were made 

 with the ratio R less than '24, as greater accuracy is obtained 

 with the larger ratios. 



6. The accuracy of the normal distribution curves was 

 tested by measuring the velocities of agitation of the 

 electrons in hydrogen with each instrument. The experi- 

 ments were made over tbe same range of forces and 

 pressures as the test experiments on the velocities in the 

 direction of the electric force. The values of k obtained 

 with the two instruments were in very close agreement, and 

 on an average they did not differ by more than 2 per cent, 

 from the values of k found in tbe previous experiments. 



It may be mentioned that in the previous experiments 

 the hydrogen was prepared by the electrolysis of barium 

 hydrate, and passed over hot copper into a drying-flask, from 

 which it was admitted through a tap into the apparatus. 

 In the test experiments with the new instruments the 

 hydrogen was admitted through a palladium tube without 

 bringing the gas into contact with any chemicals from which 

 an impurity might have been given off. There was no leak 

 in either instrument which could be detected by means of a 

 McLeod gauge, even when the apparatus was exhausted to 

 l/100th of a millimetre, and observations of the pressure 

 were made at intervals during a fortnight. 



The results obtained with hydrogen may therefore be 

 taken as being well established. 



7. The argon used in these experiments was obtained from 

 a cylinder supplied by the British Oxygen Company. The 

 gas contained about 10 per cent, of nitrogen, which was 

 removed by Rayleigh's method. It was admitted to a vessel 

 containing a solution of caustic potash, and oxygen added in 

 excess of the amount required to combine witli the nitrogen. 

 Two platinum electrodes were sealed into tubes leading into 

 the vessel, and a discharge was passed between the electrodes 

 for several hour?. The change of pressure in the gas due to 

 the combination of the oxygen and nitrogen was noted, and 

 after sparking for about fifteen hours the pressure was found 

 to remain constant. The residual traces of nitrogen were 

 removed by continuing the sparking for several hours. 

 The gas was then passed slowly over hot copper-foil and 

 into a drying vessel containing phosphorus pentoxide. 



