321 
1912-13.] Atmospheric Electric Potential Results. 
volts, so that the mean value for that hour for the month may be in error 
by about one volt. Owing to difficulties caused by the unevenness of the 
ground and the proximity of buildings, there may be a fairly large error 
in the reduction factor, which, however, does not exceed 10 per cent. Any 
error in this factor does not affect the relative values of the numbers given 
for the potential gradient, but affects the absolute values as expressed in 
volts per metre. From the observations taken outside, a factor was 
obtained by which these areas had to be multiplied to give the potential 
gradient in volts per metre. 
