396 Transactions of the Boyal Society of South Africa. 
The start was made from Bloemfontein on September 24th. Between 
that place and Vereeniging there is not much change in level, and previous 
observations have shown that the potential gradient is fairly uniform. 
From Vereeniging to Johannesburg there is a rise of 1,000 feet, and this 
is accompanied by a decided fall in the potential gradient until Germistom 
is reached, and there, considerable fluctuations are noticed, especially if a 
strong wind is blowing. In Johannesburg the changes in the value of the 
gradient are so remarkable that they will be treated separately, and the 
general results from Johannesburg to Louren9o Marques and from 
Johannesburg to Durban taken first. 
JOHANNESBUKG TO LOURENCO MaRQUES. 
After Johannesburg the first halt was made at Belfast, and here a day's 
observations were taken from 5.40 a.m. to 9.30 p.m. The country round 
Belfast is very open and free from trees, so that there were no circum- 
stances to disturb the normal potential. The sky was practically free 
from cloud all day and the potential gradient appeared to follow the 
normal course, save that the second maximum occurred at 5 p.m. instead 
of about 8 to 9 p.m. By "normal" course is meant that the potential 
rises after sunrise up to a maximum value about 8 p.m., then falls to a 
minimum and remains constant for several hours, then rises to a second 
maximum which is lower than the first, and then falls to another 
minimum, until just before sunrise on the following day. 
Table I. shows the values of the potential gradient in volts per metre 
at various times during the day. 
Table I. 
Belfast, 6,500 feet. 
Time. 
Pot. Grad. 
Time. 
Pot. Grad. 
1 rr,- 
Time. 
Pot. Grad. 
Time. 
Pot. Grad. 
5.40 a.m. 
30 
8.30 
48 
1 
1.15 
20 
5.45 
50 
5.50 
36 
9.0 
48 
1.30 
20 
6.0 
48 
6.0 
40 
9.30 
46 
2.0 
25 
6.10 
30 
6.5 
42 
10.0 
46 
2.30 
33 
6.20 
27 
6.10 
46 
10.35 
43 
2.35 
36 
7.0 
23 
6.20 
48 
11.0 
40 
: 2.50 
40 
7.15 
18 
6.30 
50 
11.30 
35 
i 3.0 
42 
7.30 
25 
6.47 
54 
11-45 
28 
3.25 
45 
7.45 
25 
7.0 
56 
12.0 
22 
3.45 
45 
8.0 
28 
7.15 
58 
12.15 P.m. 
18 
4.0 
50 
8.30 
28 
7.30 
58 
12.20 
20 
4.40 
60 
8.45 
26 
7.35 
58 
12.30 
20 
4.50 
70 
9.0 
20 
7.50 
56 
12.45 
20 
5.0 
80 
9.15 
20 
8-0 
48 
1.0 
20 
5.25 
57 
9.30 
20 
