﻿Effect of Clouds on Ionization. 



365 



middle of its swing. On pressing a key just before this lever 

 passed through the mercury a relay was worked at the next 

 passage, and the expansion was fired. Just before the nth 

 passage of the metronome lever through the mercury another 

 key was depressed, and on the nth passage a second relay 

 was actuated, which broke the current holding back the 

 pendulum. The latter then swung forward through the two 

 mercury cups ; on passing through the first it actuated 

 electromagnet E l9 thus unearthing the quadrants, and on 

 passing through the second it actuated E 2 , thus stopping the 

 charging up. It will be seen, from the numbers in r l able V., 

 that although the time of charging up w T as so short, the 

 duplicated observations are in very good agreement. 



, Table V. 



Potential on ionization-chamber —20 volts. 

 Radium in position R x (strong ionization). 



y 

 Constant value of the expansion ~ =1*331. 



Constant time of charging up of electi*ometer = 0'2o second. 

 The letters a, b, c, d, represent the order in which the 

 readings were taken. 



The mean numbers given in Table V. are shown graphi- 

 cally in fig. 4. When the age of the cloud is greater than 

 about 4 seconds the curve shows no interesting features, the 

 current simply increasing owing to the evaporation and 

 settling of the cloud and regaining its normal value in about 

 90 sees.; an inspection of the ionization-chamber after that 

 time showed that the cloud had all disappeared. 



