﻿Motion of Electrons in Argon and in Hydrogen. 1037 



were flowing through them during the time required to 

 make the observations. The distance b was found with the 

 gas at one of the lower pressures when the velocities were 

 large, and comparatively small currents were required to 

 obtain either the deflexion («-f b) or {a — b). This method 

 was found quite satisfactory with nitrogen or hydrogen in 

 the second instrument where the slit was 4 centimetres 

 from the receiving electrodes, and the distance & = *6 milli- 

 metre. 



4. With the first instrument where the slit was 2 centi- 

 metres from the receiving electrodes, it would have been 

 necessary to double the magnetic forces in order to produce 

 similar deflexions. In this case the following method was 

 used to measure the velocities in argon at the higher 

 pressures. When the centre of the stream is at a distance b 

 to the right of the electrode E 2 (figs. 1 &■ 2), the current 

 received by E 3 is larger than that received by Ej. By 

 means of a suitable magnetic force H 2 the centre of the 

 stream may be deflected through the distance b and thus 

 brought to the centre of E 2 . The two electrodes E x and E 3 

 then receive equal charges. The value of H 2 was found by 

 measuring these two charges with the central electrode 

 maintained at zero potential, and adjusting the magnetic 

 force to the point at which the charges are equal. 



The velocity W is then given by the equation 



H 2 W b 



(3) 



In order to find b, the stream is deflected in the opposite 

 direction through the distance (a — b), which is attained 

 when the current received by E 2 and E 2 is equal to that 

 received by E 3 , the required magnetic force H 3 being- 

 given by equation (2). Thus b is given by the relation 

 H 2 /H 3 = 6/(a — b), and was found to be *87 millimetre. 



In argon at the higher pressures the velocities W were 

 found by this method, and the currents necessary to produce 

 the magnetic fields H 2 were from 10 to 15 amperes. 



These results were tested by finding the velocities of 

 electrons in hydrogen with both instruments. The hydrogen 

 was admitted through palladium tubes sealed in the apparatus, 

 and the experiments were made with different forces Z and 

 pressures p, the ratio of the force to the pressure being- 

 varied from the value Z/p = '2 to Z/jo = 40. There was a 

 close agreement between the results obtained with the two 

 instruments. 



The velocities obtained for the different values of the ratio 



