252 
the author resolved to undertake the discussion of a series of 
magnetical observations, and for this purpose he selected the 
observations made at the Imperial Observatory of St. 
Petersburg, the most northern station at which hourly 
magnetical observations have been made for any lengthened 
period. Commencing, therefore, with the year 1848, the 
greatest and least values of the magnetic declination for 
every day were extracted from the observations, and taking 
the differences and arranging them in order, it was found, on 
a careful examination, that they indicated changes of activity 
taking place in a period of 3 1 days. The daily oscillations 
were then arranged in a table of 81 columns, arid taking the 
means of the numbers in these columns, their differences 
from the general mean for the year were found to be as 
follow, the unit of value being one division of the scale of 
the magnetometer, or 26'3" of arc : — 
Day. 
1 
Diff. from 
Gonoral 
Mean, 
pts. 
— 8-18 
Day. 
9 - 
Diff. from 
General 
Mean, 
pts. 
- 7-86 
Day. 
17 
Diff. from 
General 
Mean 
pts. 
+ 0-49 
Day. 
25 
Diff. from 
General 
Mean, 
pts. 
— Ill 
2 
— 
8-25 
10 - 
- 7-99 
18 
+ 635 
26 
— 
2-38 
3 
— 
332 
11 - 
- 070 
19 
- 305 
27 
— 
1:43 
4 
-b 
1-18 
12 - 
- 7-45 
20 
b 2.65 
28 
-b 
8-41 
5 
4-80 
13 - 
r 11-83 
21 
- 4-21 
29 
651 
6 
— 
0-21 
14 -1 
r 922 
22 
b 5.80 
30 
— 
6-51 
7 
- — 
1-52 
15 - 
- 119 
23 
b 339 
31 
— 
5-69 
8 
— 
G'66 
16 - 
b 599 
24 
- 508 
A projection of these numbers shows that of the seventeen 
consecutive days, 12 to 28, the amount of oscillation, or 
range of the magnetic needle, was above the mean value on 
thirteen days, and below the mean on only foitr days ; while 
of the remaining fourteen days the range was helow the mean 
on thirteen days, and above on one day only. The total 
amount of the differences for the seventeen days of maximum 
was G7 - 09, or 3’95 per day, and for the fourteen da^s of 
minimum it was 67 02, or 4*78 per day, the mean for the 
year being 39 # 8G. The ratios of the average excess of a day 
of maximum, and of the average deficiency of a day of 
