at Low Pressures. 263 



At one millimetre pressure this gives 



2 sec. 



The actual difference between the velocities of the negative 

 and positive ions in the positive column is given by 



v 2 -v 1 =X (k 2 - h) = 34-9 *Jp x 1-42 x lO 5 ^- 1 ' 5 



_ 4-95 x 10 6 



P 



These experiments were carried out in the Cavendish 

 Laboratory and my best thanks are due to Prof. J. J. Thomson 

 for his kindly interest and advice throughout the course of the 

 work. 



