210 
DR. C. CHREE: MAGNETIC DECLINATION 
Interval . 
Occurrences . 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
5 
6 
4 
4 
4 
0 
1 
3 
0 
5 
2 
2 
3 
6 
1 
Interval . 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
Occurrences. 
5 
3 
0 
2 
3 
1 
0 
3 
6 
4 
6 
5 
3 
2 
1 
Interval . 
32 
33 
34 
35 
36 
37 
38 
39 
40 
41 
42 
" 
43 
44 
45 
46 
Occurrences. 
3 
0 
0 
0 
0 
1 
1 
2 
0 
1 
0 
2 
2 
1 
0 
Interval. 
47 
48 
49 
50 
51 
52 
53 
54 
55 
56 
57 
58 
59 
Occurrences . 
0 
2 
0 
0 
1 
0 
1 
2 
0 
1 
1 
0 
0 
The number of days in the remaining 14 intervals were respectively 62, 62, 64, 65, 
76, 83, 87, 89, 93, 96, 100, 107, 112 and 272. 
In the case of the two-day or even the three-day intervals, it might occasionally he 
questioned whether the successive storms should not have been counted as one, and 
conversely what was really one storm may occasionally have been counted as two. 
Dividing the period between the first and last of the 125 storms by 124 we deduce 
30'0 days as the average interval. If, however, we omit 1890 and 1900, years in 
which storms were very scarce, the average interval is reduced to 27'8. This should 
be borne in mind when considering the significance of the considerable number of 
times when the interval lay between 25 and 28 days. 
§ 8. The disturbed days were not absolutely the only ones excluded from the 
computation of the regular diurnal variation. A very small number of days had to 
be excluded through stoppage of the clock or other misadventure. When only a few 
hours’ trace had been lost during a quiet time, data were interpolated with the 
assistance of the Falmouth curves, kindly lent by Mr. Kitto. 
With a view to the study of sunspot influence on the magnetic state of individual 
days, it was important to have a complete set of values of the absolute daily range 
(maximum less minimum). Stoppage of the clock—a rare occurrence—may conceal 
the exact time of the maximum or minimum, but it does not hide the extent of the 
range. In most cases of a short failure of trace one could be absolutely certain, 
having regard to the corresponding Falmouth curve, that neither maximum nor 
minimum was involved. But in a certain number of cases, especially in January 
during the determination of the scale values, there was some slight uncertainty, and 
in these cases the range was taken from the Falmouth curves. This raises no 
