the Motion of Electrons in Gases. 



875 



three electrodes E 1? E 2 , E 3 at a distance of 4 centimetres 

 from the plate B. 



A -= 



Fig. 1. 



B 

 G 



The electrodes E 1? E 2 , E 3 are mounted on ebonite fixed 

 to the brass ring C 4 , and the upper surfaces turned so that 

 they should all be in the same plane, parallel to the plates 

 A and B. 



The electrodes E lt E 2 , E 3 are sections of a disk 7*6 centi- 

 metres in diameter. The central electrode E 2 is a strip 

 4*5 millimetres wide insulated by gaps half a millimetre 

 wide from the electrodes E 2 and E 3 . 



It is essential that the field below B should be perfectly 

 uniform, and for this purpose the brass rings Ci, 2 , G 3 are 

 fixed at equal intervals apart between the plate B and the 

 ring C 4 , and maintained at constant potentials by i battery 

 of small accumulators. The positive terminal of the battery 

 Is connected to the ring 4 which is at zero potential, and 

 the rings C l5 C 2 , C 3 and the plates A and B are connected to 

 points of the battery which maintain them at negative poten- 

 tials proportional to their distances from the lower ring C 4 . 

 Thus the electrons arriving at the slit in the plate B have 

 acquired the final velocity corresponding to a constant electric 

 force Z, and continue to move under the same force from the 

 slit to the electrodes E 1? E 2 , E 3 , The stream diverges and a 

 large proportion of the electrons are received on the elec- 

 trodes E t and E 3 , although the central electrode E 2 is much 

 wider than the slit in B. 



3M 2 



