Variation in Value of Atmospheric Electrical Potential. 401 
of above 8 miles. The potential varied from 400 to 500 volts per metre, and, 
making allowance for trees, was practically constant. Observations were 
taken on the beach facing the Indian Ocean. A strong wind was blowing 
at the time, and considerable fluctuations were noticed and found to be 
due to the sand blown by the wind. Standing in the water the positive 
potential gradient was about 500 volts per metre, but this fell on walking 
in the direction the wind was blowing to 140, and rose again on passing 
beyond the range of the blown sand. 
The maximum value of the potential gradient was 500 volts per metre, 
and the minimum a little under 300. The range is thus smaller than 
usually found, but this may have been due to the mist, which was present 
most of the day. 
On the return journey to Johannesburg observations were taken at the 
places given in Table VI. ; the values of the potential gradients are those 
actually observed. At times mist was present. The values are of quite a 
different order from those recorded for Durban, Pietermaritzburg, or 
Lourengo Marques. 
Observations taken between Pietermaritzburg and Johannesburg give 
the following : — 
Table VI. 
October 4cth. 
Altitude. 
Time. 
Pot. Grad. 
4,320 
6.0 a.m. 
60 
4,429 
55 
3,893 
7.30 „ 
90 
4,414 
8.35 „ 
60 
4,554 
8.50 „ 
48 
4,983 
9.10 „ 
45 
5,225 
9.30 „ 
45 
5,386 
40 
5,429 
10.0 „ 
45 
5,413 
10.29 „ 
37 
Paardekop 
5,652 
11.10 „ 
35 
5,022 
12.40 p.m. 
50 
Val 
5,160 
1.50 „ 
50 
5,275 
3.0 „ 
40 
5,026 
4.0 „ 
40 
Nigel 
5,041 
4.20 „ 
40 
These values do not indicate much, and owing to the different times at 
which they were taken the results are not comparable, but they show a 
very marked difference from those taken at sea-level and at Maritzburg. 
