325 
1912-13.] Atmospheric Electric Potential Results. 
of the year, and also the 
total range of the varia- 
tion, while the last row 
shows the number of 
curves measured each 
month. It is to be noted 
that during the last three 
weeks of August the 
apparatus was not in 
operation owing to the 
vacation, and the mean 
values for that month 
have been deduced from 
a few days at the be- 
ginning of the month, 
several of which were 
far from typical of the 
season of the year. In 
fig. 3 a graphical repre- 
sentation of this varia- 
tion is shown for each 
month ; and for the 
whole year and the two 
half-years October to 
March and April to 
September, in fig. 4. 
An examination of 
these curves shows that 
they all have a minimum 
in the early morning 
about 4 a.m., whereas 
the other part of the 
curve varies considerably 
throughout the year. In 
mid- winter the curve 
approximates roughly to 
a single sine curve with 
a maximum in the after- 
noon ; as the year ad- 
vances, the time of occur- 
A.M. 
Jan. 
Feb. 
M ar. 
Apr. 
May 
June 
July 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
12 2 4 6 8 10 12 2 4 6 8 10 12 
Fig. 3. 
