64 
MR. AIRY ON THE OBSERVED DEVIATIONS OF THE COMPASS 
quotient is 12° 47'. On examining- the ‘^Mean of Polar-Magnet-Deviations” at the 
foot of the columns of the Table, it is found that the Mean corresponding to Modulus 
0-34 is 12° 35', and that corresponding to Modulus 0'35 is 12° 58'. Hence the 
Modulus for mean 12° 47' is 0-3452. 
8 & 9. The neutral position being 0^-73, the ‘‘ Apparent Inclination from Neutral 
Position” for azimuth of ship’s head OP will be 31P-27 ; and so for the others. Then 
two series of numbers are interpolated from the Table of Polar-Magnet-Deviations 
for the fractional parts of the points ; one for Modulus 0*34, and the other for 
Modulus 0*35. Between the pairs of corresponding numbers thus found, a third 
interpolation is made for the fractional part of the Modulus, to 0-3452 ; and thus are 
obtained the Tabular Polar-Magnet-Deviations required. Subtracting these from 
Apparent 
azimuth of 
ship’s 
head. 
Apparent 
inclination 
from 
neutral 
position. 
Tabular polar-magnet-deviation. 
Excess of 
corrected 
observed 
deviation. 
One-fifth of 
quadrantal 
group. 
Modulus 
0-34. 
Modulus 
0-35. 
Modulus 
0-3452. 
P 
P 
— 2 47 
o / 
o / . 
0 
31-27 
— 2 52 
- 2 50 
(-0 7) 
1 
0-27 
-t- 1 2 
+ 1 4 
+ 1 3 
+ 2 35 
2 
1-27 
+ 4 49 
+ 4 57 
+ 4 53 
+ 4 20 
3 
2-27 
-F 8 26 
+ 8 40 
+ 8 33 
+ 3 57 
o f 
+ 3 57 
4 
3-27 
+ 11 45 
+ 12 6 
+ 11 56 
+ 3 52 
5 
4-27 
+ 14 38 
+ 15 5 
+ 14 52 
+ 2 46 
6 
5-27 
+ 16 59 
+ 17 31 
+ 17 16 
+ 2 12 
7 
6-27 
+ 18 42 
+ 19 16 
+ 19 0 
+ 0 3 
8 
7-27 
+ 19 40 
+ 20 16 
+ 19 59 
(-1 21) 
9 
8-27 
+ 19 51 
+ 20 27 
+ 20 10 
—2 57 
10 
9-27 
+ 19 14 
+ 19 50 
+ 19 33 
—3 45 
11 
10-27 
+ 17 52 
+ 18 24 
+ 18 9 
-4 1 
12 
11-27 
+ 15 48 
+ 16 16 
+ 16 3 
— 3 35 
— 3 33 
13 
12-27 
+ 13 9 
+ 13 32 
+ 13 21 
— 1 53 
14 
13-27 
+ 10 0 
+ 10 18 
+ 10 9 
— 0 51 
15 
14-27 
+ 6 31 
+ 6 42 
+ 6 37 
— 0 44 
16 
15-27 
+ 2 47 
+ 2 52 
+ 2 50 
( — 0 22) 
17 
16-27 
— 1 2 
— 1 4 
— 1 3 
+ 1 1 
18 
17-27 
- 4 49 
— 4 57 
— 4 53 
+ 2 21 
19 
18-27 
— 8 26 
— 8 40 
— 8 33 
+ 2 41 
20 
19-27 
— 11 45 
— 12 6 
— 11 56 
+ 2 44 
+ 3 19 
21 
20'27 
— 14 38 
— 15 5 
— 14 52 
+ 2 58 
22 
21-27 
-16 59 
-17 31 
-17 16 
+ 2 39 
23 
22-27 
— 18 42 
— 19 16 
-19 0 
+ 2 11 
24 
23-27 
-19 40 
—20 16 
-19 59 
( + 0 57) 
25 
24-27 
— 19 51 
— 20 27 
— 20 10 
-0 14 
26 
25-27 
-19 14 
-19 50 
-19 33 
-2 14 
27 
26-27 
— 17 52 
— 18 24 
-18 9 
-4 3 
28 
27-27 
— 15 48 
-16 16 
— 16 3 
-3 59 
—3 30 
29 
28-27 
-13 9 
— 13 32 
-13 21 
— 3 11 
30 
29-27 
— 10 0 
— 10 18 
— 10 9 
— 2 53 
31 
30-27 
— 6 31 
— 6 42 
— 6 37 
— 0 57 
the corrected observed deviations, we have the excess, which clearly follows with 
considerable accuracy, a Positive Quadrantal law, perhaps slightly disturbed by the 
residual small terms in the manner explained above. Its Mean Coefficient is +3° 35' 
or OP-3185, whose equivalent in abstract number is -l-0-0626 = P. 
2 
10. From these numbers, ^ quadrantal coefficient X sine of twice approximate 
