Distribution of Electric Force at Low P 



ressure 



183 



The force per unit deflexion of the spot is given by 



2V 



X' 



-6 + i) 



Therefore by multiplying the actual deflexion of the spot 

 by X' the value of the force in the field through which the 

 rays have passed is obtained. If V is measured in volts, X 

 is found in volts/cm. In the present work d is taken as the 



diameter of the discharge-tube. 



Apparatus. 



Two types of apparatus were used. The final form is 

 shown in fig. 1. The discharge took place in the tube M 



Fig. I. 



Wllemi'te 



w 



To earth 



To mercury pump, P 2 C 5 drying tube 

 tWleca gauge ^charcoal bulb. 



between parallel plate electrodes which were capable of 

 being moved up and down the tube whilst being kept at a 

 fixed distance apart. 



The beam of cathode rays was produced in S, passing from 



