Variation of Atmospheric Electrical Quantities. 285 



Fig. l.—Kew, 1914. 

 Mean Diurnal Variation (May, June, July) (unsinoothed). 



Noon 

 7h. 8 9 10 II 12 13 14 15 16 17 18 19 20 



(+ Charge 

 per c.cjxh 

 in e. m. u. 



Conductivity X 10 

 in e. m. u. 50 



40 



120 

 (Air-Esrth 

 Current)XIO } 00 

 in amp./cm. 2 ' QQ 



300 

 250 



Potential 200 



volts/metre 



1 150 



1-0 



Mobility q.q, 

 cm./sec. 



Potential 200 

 Normal 

 (1898-1912) l5 ° 





Monthly Means for May, June, and July, 1914. 

 From the results for May given in Table I., there is a 

 minimum for the positive charge at 9 a.m. and two almost 

 equal maxima at 11 a.m. and 2 p.m., while the conductivity 

 shows a well-marked minimum at 8 a.m. and maximum at 

 4 p.m. The air-earth current shows a minimum at 8 A.M., 

 which corresponds with a maximum of potential. The po- 

 tential is low during the afternoon with a minimum at 1 p.m., 

 while the mobility increases gradually during the day. For 

 June the positive charge has a maximum value at noon, and 

 two minima at 9 a.m. and 7 P.M., which correspond with the 

 times for minima in the conductivity. As usual, the maxi- 

 mum for the positive charge precedes that for conductivity 

 by a few hours. The air-earth current varies somewhat 

 similarly to the potential, and the mobility increases during 

 the day to a maximum at 5 p.m. 





