Stages of Ionization by Collision. 



967 



In order to obtain a measurement o£ p the electrodes 1, 2, 

 and 3 were earthed, and the lower plate was connected to 

 the battery. The earth connexion was then removed and 

 the electrometer was put into connexion with the inside 

 cylinder of K x . The ultra-violet light was turned on for a 

 period of time depending on the magnitude of «, and the 

 slider S was moved until the electrometer needle was brought 

 back to its zero position. This could be done with great 

 accuracy by using the adjustable resistance It. The electro- 

 meter was then switched on to the inside cylinder of K 2 , and 

 Hi and R 2 were adjusted so that the electrometer needle was 



again brought to the zero position. The ratio p 2 ~p was 



±tj -p xt 2 



taken as a first approximation, and several more readings 

 were taken to obtain an exact value. 



The curves in fig. 4 represent the results of the experiments 



Fig. 4. 





























1 























/ 



' 























V 



/ 





7 



















A 



/ 

























p 























A 













T 





















































































/ 



// 



















2L 



made with air at pressures of 2, 3, 4, and 5 mm. of mercury. 

 The air was dried very thoroughly by allowing it to remain 

 in the reservoir for some weeks. 



The theory requires that the rays should fall symmetrically 

 on the electrode 2. In order to obtain this condition of 

 symmetry the leads from electrodes 1 and 3 were connected 

 with the inside cylinders of K x and K 2 respectively, electrode 

 2 was earthed, and the apparatus was moved (the slightest 

 motion was found to be sufficient) relative to the spark-gap 



3 S 2 



