Vertical Component of Magnetic Force. 
241 
tember till December. The diminution from January till December is 0-001731 ; if we refer to the previous 
attempt to connect the different series of observations, we find the mean annual diminution from the beginning 
of March 1843 till the beginning of March 1844 =213 micrometer divisions ; this, together with the rate of 
this change, will give 210 micrometer divisions (= 0-001890) for the diminution from January 1843 to January 
1844. If proportional parts of this be applied to the monthly means above, the secular change will be elimi- 
nated, and the annual period rendered more distinct. The corrected means are as follow : — 
Jan. Feb. March. April. Slay. June. July. Aug. Sept. Oct. Nov. Dec. 
0-01 I 6924 6899 6690 6555 6539 6771 6798 6793 6599 6716 6852 6925 
This indicates a maximum at mid-winter and at mid-summer, a minimum about April and a minimum in 
September. It seems, therefore, very probable that the same law holds for the vertical component as has al- 
ready been shewn to exist for the horizontal component, namely, maxima at the solstices, and minima at the 
equinoxes. 
From the above the minima at the equinoxes seem to differ little, but the maximum at the winter solstice 
is considerably greater than that at the summer solstice. 
The range of the annual period is 0-000386. 
TABLE XVI. — Mean Variations of the Vertical Component of Magnetic Force, after eliminating the 
Secular Change, with reference to the Moon's Age, Declination, and Distance from the Earth, 
for 1843. 
Variations 
Variations 
After 
Variations 
After 
Variations 
Before 
Variations 
Before 
Variations 
Moon's 
of Ver- 
Moon's 
of Verti- 
Moon 
of Verti- 
Moon 
of Verti- 
and 
of Verti- 
and 
of Verti- 
Age. 
tical Com- 
Age. 
cal Com- 
farthest 
cal Com- 
farthest 
cal Com- 
after 
cal Com- 
after 
cal Com- 
ponent. 
ponent. 
North. 
ponent. 
North. 
ponent. 
Perigee. 
ponent. 
Apogee. 
ponent. 
Day. 
0-000 
Day. 
0-000 
Day. 
0-000 
Day. 
0-000 
Day. 
0-000 
Day. 
0-000 
15 
055 
6 
025 
0 
136 
14 
077 
7 
118 
7 
078 
16 
056 
1 
017 
1 
094 
15 
063 
6 
108 
6 
054 
17 
081 
2 
050 
2 
151 
16 
046 
5 
191 
5 
067 
18 
057 
3 
076 
*> 
O 
096 
17 
013 
4 
101 
4 
067 
19 
048 
4 
035 
4 
091 
IS 
035 
3 
071 
3 
041 
20 
077 
5 
024 
5 
060 
19 
013 
2 
078 
2 
043 
21 
076 
6 
147 
6 
062 
20 
020 
1 
107 
1 
053 
22 
058 
7 
045 
7 
069 
21 
016 
P 
073 
A 
055 
23 
076 
8 
068 
8 
067 
22 
012 
1 
071 
1 
000 
24 
057 
9 
057 
9 
047 
23 
030 
2 
105 
2 
046 
25 
090 
10 
049 
10 
040 
24 
000 
3 
105 
3 
064 
26 
071 
11 
062 
11 
031 
25 
062 
4 
091 
4 
114 
27 
028 
12 
000 
12 
055 
26 
045 
5 
090 
5 
114 
28 
144 
13 
009 
13 
090 
27 
090 
6 
046 
6 
129 
29 
051 
14 
011 
7 
064 
7 
110 
Table XVI. was formed from Table XV. in the manner already indicated, Table II. for the declination. 
Variations of the Vertical Component of Magnetic Force with reference to the relative 
Positions of the Sun, Moon, and Earth, as indicated by the Moon's Age. 
The means shew, with considerable irregularities, maxima near the quadratures, and minima near the 
syzigies. The principal minimum occurs at the period of full moon, the following- means of groups give the 
same result : — 
14 days to 16 days, Full Moon, 0-000041 
17 20 ... 0-000066 
21 24 ... 0-000067 
25 28 ... 0-000083 
29 days to 1 day, New Moon, 0-000031 
2 5 ... 0-000046 
6 9 ... 0-000079 
10 13 ... 0-00003. 
JI.VG. AND MET. OBS. 1843. 3 P 
