﻿Metres. 

 20-40 

 40-60 



ad 



given 



686 Dr. A. S. Eve and Mr. F. H. Day on the 



fixed electroscope was placed on a table 40 m. from the 

 source, and the stations for the movable electroscope were 

 in a straight line at 20, 40, 60, 80 metres from the bulb, out 

 of doors, on the College Campus. 

 The values obtained were : 



X. 



•00027 

 •00014 (?) 



This bulb had given a mean value '00029 within the 

 building. Just as the readings at 60 m. were nearing com- 

 pletion, the bulb fractured near the cathode, and so there is 

 some uncertainty as to the value of X between 40 and 60 m. 



On the day following the steady bulb (B) was used with 

 results i 



Metres. X. 



20-40 '00040 



40-60 -00029 



60-80 '00010 



This bulb had given within the building '0004. The 

 maximum alternative spark-gap was 11 cm. 



The readings taken at the 80 m. station are not very 

 accurate, for although the leaf was moving at the rate of 

 18 divisions a minute, there were troublesome convection 

 currents due to a warm sun and a cold wind. The readings 

 were taken in January, when there were 10 cm. of snow on 

 the ground and the temperature was — 6° C. Under suit- 

 able meteorological conditions it will be possible to take 

 readings up to 150 m,, and to decide whether there is really 

 a decrease in the value of X for increased distance as these 

 results seem to indicate. This work we hope to undertake 

 in the spring. 



Total number of Ions. 



If the number of ions produced in a cubic centimetre in a 

 second is q, at a distance r from the bulb, we have 



* - \r 



and the total number of ions produced in a second is 



k ' = 2tt£/\. 



*.£> 



, e 



The constant k is the (theoretical) number of ions produced 

 in 1 cubic centimetre at 1 centimetre distance from the 

 focus on the anticathode. 



The electroscopes were calibrated by the ionization due to 



