74 
THE REV. STEPHEN J. PERRY ON MAGNETIC OBSERVATIONS 
Table II. 
Semiannual inequality of the Dip. 
Date. 
Correction 
for secular 
variation. 
Mean 
+ secular 
variation. 
Observed 
values. 
Observed- 
April to 
September. 
Calculated. 
October to 
March. 
July 1, 1863 
+ 5 53 
69 51 14 
69 49 32 
-1 42 
Jan. 1. 1864 
+ 4 59 
50 20 
48 1 
-2 19 
July 1, 1864 
+ 4 4 
49 25 
48 2 
-1 23 
Jan. 1, 1865 
+ 3 10 
48 31 
49 3 
+ 0 32 
July 1 , 1865 
+ 2 15 
47 36 
50 16 
+ 2 40 
Jan. 1, 1866 
+ 1 21 
46 42 
48 58 
+ 2 16 
July 1, 1866 
+ 0 27 
45 48 
47 29 
+ 1 41 
Jan. 1, 1867 
-0 27 
44 54 
46 30 
+ 1 36 
July 1, 1867 
- 1 21 
44 0 
45 18 
+ 1 18 
Jan. 1, 1868 
-2 15 
43 6 
43 58 
+ 0 52 
July 1, 1868 
-3 10 
42 11 
40 18 
-1 53 
Jan. 1, 1869 
-4 4 
41 17 
41 47 
+ 0 30 
July 1, 1869 
-4 59 
40 22 
39 5 
-l 17 
Jan. 1, 1870 
-5 53 
39 28 
36 38 
-2 50 
Mean differences in the semiannual periods 
-0 5 
+ 0 5 
The resulting difference is small compared with the errors of observation, and there- 
fore it can afford but a slight confirmation of the hypothesis of the dependence of this 
inequality on the position of the sun in the ecliptic. 
Table III. 
Residual errors in the monthly mean values of the Dip. 
1863- 
-64. 
1864-65. 
1865 
-66. 
1866 
-67. 
1867 
-68. 
1868-69. 
1869 
-70. 
Mean. 
Semiannual 
mean. 
April 
-0 
// 
21 
-3 
// 
15 
+ 2 
// 
2 
+ 2 
46 
+ 1 
// 
0 
/ 
-1 
43 
+ 3 
19 
+ 0 
33 
> 
[ 
May 
2 
48 
— 2 
55 
+ 2 
56 
+ 1 
29 
+ 0 
8 
-1 
10 
— 2 
55 
-0 
45 
June 
-3 
26 
-0 
11 
+ 1 
44 
+ 1 
45 
-0 
37 
— 2 
13 
— 1 
35 
-0 
39 
l / „ 
>-0 1 
July 
+ 0 
10 
-1 
33 
+ 3 
1 
+ 2 
53 
+ 3 
34 
+ 0 
10 
2 
2 
+ 0 
53 
August 
-1 
>-* 
/ 
-1 
39 
+ 3 
49 
+ 0 
49 
+ 2 
34 
-4 
54 
+ 0 
47 
+ 0 
3 
1 
September ... 
2 
34 
+ 1 
36 
+ 2 
50 
+ 0 
50 
+ 1 
44 
-0 
58 
-4 
38 
-0 
10 
J 
October 
— 2 
26 
-0 
39 
+ 3 
54 
+ 1 
54 
+ 0 
1 
+ 1 
21 
— 4 
37 
-0 
5 
November ... 
-2 
10 
+ 0 
32 
+ 1 
38 
+ 1 
21 
+ 1 
11 
+ 0 
51 
+ 0 
8 
4-0 
30 
1 
December ... 
-3 
14 
+ 1 
16 
+ 0 
13 
+ 1 
42 
-0 
14 
+ 0 
27 
-3 
32 
-0 
29 
> + 0 0-5 
January 
-3 
1 
-1 
17 
+ 0 
38 
+ 1 
59 
+ 0 
35 
+ 1 
19 
-6 
10 
-0 
51 
February ... 
- 1 
0 
+ 1 
41 
+ 3 
3 
+ 0 
34 
+ 2 
12 
— 1 
0 
— 3 
1 
+ 0 
21 
March.... 
— 2 
45 
+ 1 
3 
+ 3 
38 
+ 1 
40 
+ 1 
3 
-0 
15 
-0 
2 
+ 0 
37 
J 
Means 
-2 
4 
-0 
27 
+ 2 
27 
+ 1 
39 
+ 1 
6 
-0 
40 
-2 
2 
In this Table the evidence is still stronger than before that the correction applied 
from July 1864 to March 1868 is in excess. 
The probable errors deduced from the above Table are : 
for any single monthly value +l /, 45, 
and for the deduced means -f-O'TG. 
