IN THE LARGER MAGNETIC DISTURBANCES. 
175 
tudes, where the north end of the needle attains its extreme easterly and westerly 
positions at the same hours in all seasons, at St. Helena the curve of diurnal 
movement is precisely reversed at opposite periods of the year ; in general terms, it 
may be said to correspond to that of the diurnal variation in the northern hemisphere, 
(at Toronto for example), when the sun is north of the equator, and to the diurnal 
variation in the southern hemisphere (or as at Hobarton), when the sun is south of 
the equator. It appeared therefore desirable to examine whether the law of the 
occurrence of the disturbance, as respects the hour of the day, remained the same in 
every month in the year, whether in fact there was any analogy between the law of 
hourly disturbance at one period of the year compared with northern latitudes, or at 
Toronto, and of the opposite period compared with southern latitudes, or at Hobarton. 
Table X. will show that the law is the same in all the months of the year, the 
hours of the day being in every month periods of greatest, and the night hours of 
least disturbance. 
Table X. 
Monthly Statement of the number of Disturbed Observations in Five Years, at St. 
Helena, distributed into the several months and hours of their occurrence. 
Jan. 
Feb. 
March . 
April. 
May. 
June. 
July. 
August. 
Sept. 
Oct. 
Nov. 
Dec. 
Sums. 
Hours. 
Noon. 
34 
30 
28 
42 
16 
11 
32 
19 
25 
13 
20 
30 
300 
1 
26 
24 
29 
42 
25 
12 
32 
19 
34 
19 
23 
28 
313 
2 
29 
31 
20 
35 
20 
12 
21 
22 
37 
12 
27 
28 
294 
3 
28 
30 
18 
23 
23 
10 
25 
13 
29 
12 
17 
26 
254 
4 
28 
22 
18 
18 
16 
6 
21 
12 
21 
12 
14 
18 
206 
5 
16 
10 
14 
12 
8 
5 
9 
9 
16 
10 
11 
11 
131 
6 
7 
5 
8 
7 
5 
0 
6 
6 
3 
3 
6 
11 
67 
7 
3 
2 
4 
8 
1 
1 
3 
1 
2 
0 
4 
3 
32 
8 
3 
1 
5 
6 
3 
2 
3 
3 
1 
2 
3 
3 
35 
9 
4 
1 
3 
6 
2 
1 
1 
2 
0 
0 
2 
2 
24 
10 
4 
2 
2 
6 
2 
0 
1 
3 
0 
0 
1 
2 
23 
11 
3 
1 
3 
6 
2 
0 
2 
1 
0 
0 
2 
2 
22 
Midnt. 
3 
2 
2 
6 
3 
0 
2 
0 
0 
0 
2 
4 
24 
13 
1 
2 
o 
4 
0 
0 
2 
0 
1 
1 
2 
2 
17 
14 • 
1 
2 
2 
2 
1 
0 
3 
0 
1 
2 
3 
2 
19 
15 
2 
1 
1 
2 
1 
0 
2 
3 
1 
1 
3 
1 
18 
16 
3 
2 
0 
2 
1 
1 
1 
2 
1 
1 
3 
0 
17 
17 
3 
1 
0 
2 
0 
0 
4 
1 
1 
2 
5 
0 
19 
18 
3 
1 
0 
2 
2 
1 
2 
3 
3 
2 
5 
1 
25 
19 
5 
2 
1 
2 
1 
2 
5 
3 
11 
10 
5 
2 
49 
20 
15 
8 
8 
9 
4 
1 
5 
6 
26 
15 
4 
5 
106 
21 
22 
15 
12 
16 
18 
4 
9 
10 
26 
14 
13 
16 
175 
22 
27 
24 
17 
18 
17 
5 
17 
11 
15 
19 
18 
25 
213 
23 
27 
38 
25 
28 
16 
7 
25 
20 
17 
20 
22 
31 
276 
Sums. 
297 
257 
222 
304 
00 
81 
233 
169 
271 
170 
215 
253 
2659 
It now only remains to notice the influence of the disturbances on the mean posi- 
tion of the magnet at the different hours ; this we shall determine by obtaining the 
aggregate excess of disturbance in one direction over that in the opposite direction, 
2 A 2 
