THE COMPASS-NEEDLE ON THE DEVIATIONS OF THE COMPASS. 
181 
The maximum deviation found was 7° 60'. The coefficients of deviation obtained were 
A. B. C. D. E. F. a. n. K. 
0/ O I O I O/ O / O / O J O I O I 
+0 38 —1 53 -2 55 -2 28 +0 48 +0 12 -fO 4 -f 3 16 —0 4 
Probably nearly all these errors would have been avoided if the Admiralty Standard 
card had been used ; for it is to be observed that the introduction of the errors depend- 
ing on the length of the needle not only affects the deviations directly, but affects them 
indirectly, by disguising and preventing the proper correction of the semicircular and 
quadrantal errors. 
Since this paper was read we have also made the following experiment : — 
Two 6-inch bar magnets were placed at distances of 1 ft. If in. to the east and west 
of the centre of the needle, the north end of each bar magnet being directed to the 
north. Three similar bar magnets tied together were placed with their centres at a 
distance of 1 ft. 5| in. north of the centre of the needle, and with their ends directed to 
the north. In this position they were found to correct, as nearly as possible, the semi- 
circular delation caused by the first two bars. The following Table gives the results 
of obsen’ation on needles of different kinds. In this experiment the superiority of the 
Admiralty Standard compass card to the others was very marked. 
Correct mag- 
netic direction 
of bar magnet. 
3-inch single 
needle. 
6-ineli single 
needle. 
il2-inch single 
needle. 
2-needle card, 
each needle 
5^ inches. 
2-needle card, 
each needle 
8^ inches. 
Admiralty 
Standard 
compass card. 
North. 
O 
0 
10 
W. 
O 
0 
10 
E. 
O 
0 
/ 
5 
E. 
O 
0 
10 
W. 
O 
0 
10 
E. 
O 
0 
45 
w. 
N. 30° E. 
0 
15 
E. 
2 
45 
E. 
10 
55 
E. 
1 
10 
W. 
0 
10 
W. 
0 
45 
w. 
N. 60° E. 
0 
25 
W. 
0 
10 
\V. 
7 
35 
E. 
0 
20 
W. 
0 
15 
V/. 
0 
40 
w. 
East. 
1 
5 
W. 
3 
15 
W. 
11 
45 
W. 
1 
10 
E. 
2 
0 
E. 
0 
25 
w. 
S. 60° E. 
0 
0 
0 
15 
E. 
1 
50 
E. 
0 
10 
E. 
0 
0 
0 
20 
w. 
S. 30° E. 
0 
45 
E. 
3 
10 
E. 
11 
45 
E. 
0 
0 
1 
10 
E. 
0 
10 
E. 
South. 
0 
10 
^V. 
0 
25 
W. 
2 
0 
W. 
0 
15 
E. 
1 
0 
E. 
0 
0 
S. 30° W. 
1 
25 
W. 
3 
30 
W. 
11 
30 
W. 
1 
5 
E. 
1 
0 
E. 
0 
0 
S. 60° W. 
0 
25 
W. 
0 
10 
W. 
1 
0 
w. 
0 
10 
E. 
1 
0 
E. 
0 
0 
V'est. 
0 
30 
E. 
3 
0 
E. 
12 
45 
E. 
1 
0 
W. 
0 
50 
VV. 
0 
10 
W. 
N. 60° W. 
0 
5 
W. 
0 
25 
W. 
9 
35 
W. 
0 
0 
0 
55 
E. 
0 
10 
W. 
N. 30° W. 
1 
0 
W. 
3 
10 
\V. 
10 
45 
W. 
0 
40 
E. 
0 
40 
E. 
0 
20 
W. 
From these values the following are the coefficients obtained. 
A. 
B. 
C. 
D. 
E. 
F. 
G. 
H. 
K. 
L. 
M. 
3 inch single needle... 
O 
-0 
16 
O 
0 
2 
o 
0 
1 
O 
-0 
/ 
15 
O 
0 
/ 
3 
O 
0 
50 
O 
0 
/ 
1 
0 
19 
O 
0 
5 
0 
1 
O 
0 
/ 
0 
^ 
-0 
8 
0 
6 
0 
2 
-0 
7 
-0 
6 
3 
8 
0 
12 
— 0 
5 
0 
0 
-0 
5 
0 
3 
9> 3l 
0 
1 
2 
32 
-0 
14 
1 
52 
— 0 
1 
11 
34 
0 
40 
-2 
28 
0 
14 
-3 
13 
-0 
12 
5^5 „ double needle... 
0 
4 
0 
3 
-0 
21 
-0 
9 
0 
2 
-0 
38 
0 
3 
-0 
4 
-0 
1 
0 
10 
0 
7 
^8 » >) » 
0 
33 
0 
9 
-0 
24 
-0 
10 
0 
5 
-0 
52 
— 0 
5 
-0 
7 
0 
2 
0 
43 
0 
4 
Admiralty Standard ... 
-0 
17 
-0 
6 
-0 
21 
-0 
5 
0 
0 
-0 
10 
-0 
3 
-0 
3 
-0 
3 
0 
3 
0 
1 
