148 DR. C. CHEEE: ATMOSPHERIC ELECTRICITY POTENTIAL GRADIENT 



intervening minimum diminish as we approach midwinter. But the transition is so 

 gradual that it is difficult to draw a line between summer and winter months. This 

 is one of the reasons for dividing the year into three seasons. 



JAM 



FES 



MAR APRIL MAY JUNE JULY AUGUST SEPT OCT NOV DEC 



APRIL MAY JUNE JULY AUGUST SEPT 



Fig. 3. Isopleths. 



. Potentials above mean. 



below 

 Times of sunrise and sunset. 



OCT 



NOV 



DEC 



The November, December, and January curves are of very similar type. The 

 February curve resembles the March curve almost as closely as it does the January 



