329 
1912-13.] Atmospheric Electric Potential Results. 
As, however, the mean value of the potential gradient for the month varies 
with the month, it is also advisable to examine the values of the ratios 
aja 0 and a 2 /a 0 , and these are also tabulated in Table III. It will be seen 
that aja 0 is high in the winter, having a maximum in February, a low value 
Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. 
Fig. 6. — I. Annual Variation of a r II. Annual Variation of a 2 . 
Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. 
Fig. 7. Annual Variation of a 2 Time of Sunrise. 
in the summer, and a minimum in September, while aja 0 has a maximum in 
August and a minimum in January. 
The annual variation of the phase of the 24-hour wave is shown in 
fig. 7 ; it is a minimum in winter and a maximum in summer. The 
extremely high value of a 1 in August must be regarded as untrustworthy, 
as the number of curves measured for August was, as mentioned before, 
