94 
LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
of the smaller value of a to those observations which were made when the ship was 
in progress from the lower to the higher latitudes. If a be taken as it was found at 
Hobarton and the Falkland Islands, not only are the differences generally greater, 
but they are systematically so ; evidencing an over compensation where the north 
and south points are approached; whilst with the smaller value of a the differences 
are greatly diminished in amount, and exhibit no appearance whatsoever of system. 
They are such as may well be supposed to have been occasioned partly by observation 
error, and partly by small differences of geographical position in which the observa- 
tions themselves were made. 
Ship’s head 
by compass. 
Number 
of obser- 
Inclination 
observed. 
Values of the Constants. 
a=+-028. 
* = + •984 ; e=+-015; d= 1. 
Values of the Constants. 
a= +’023. 
* = +•984; c=+-015; d= 1. 
vations. 
| 
Computed Inclinations 
corrections, corrected. 
a — P. 
Computed 
corrections. 
Inclinations 
corrected. 
u — l 3. 
N. 
1 
— 80 58 
+ 1 32 
P. 
— 79 26 
— 20 
° 
+ 1 16 
P. 
—79 42 
— 3 
N.N.E. 
2 
— 81 00 
+ 1 27 
-79 33 
-13 
+ 1 12 
-79 48 
+ 3 
N.E. 
2 
— 80 42 
+ 1 12 
-79 30 
—26 
+ 1 00 
-79 42 
— 3 
N.W. 
3 
-80 35 
+ 1 12 
-79 23 
-23 
+ 1 00 
-79 35 
-10 
n.e. by e. 
2 
— 80 50 
+ 1 01 
-79 49 
+ 3 
+ 0 55 
-79 55 
+ 10 
w. 
1 
-79 58 
+ 0 17 
-79 41 
— 5 
+ 0 14 
-79 44 
— 1 
E. 
3 
-79 50 
+ 0 17 
-79 33 
-13 
+ 0 14 
-79 36 
- 9 
e. by s. 
1 
-79 45 
-0 01 
-79 46 
-00 
-0 01 
-79 46 
+ 1 
| s.w. by w. 
3 
-79 19 
-0 38 
-79 57 
+ 11 
— 0 31 
-79 50 
+ 5 
f s.w. | w. 
1 
-79 30 
— 0 42 
-80 12 
+ 26 
— 0 34 
-80 04 
+ 19 
\ s.w. \ w. 
1 
-79 10 
— 0 46 
-79 56 
+ 10 
— 0 38 
-79 48 
+ 3 
I S.E. 
1 
-79 08 
— 0 55 
— 80 03 
+ 17 
— 0 45 
-79 53 
+ 8 
S.W. 
3 
— 78 52 
— 0 55 
-79 47 
+ l 
— 0 45 
-79 37 
— 8 
s.w. % s. 
1 
-78 48 
— 1 02 
-79 50 
+ 4 
— 0 50 
-79 38 
- 7 
S.S.E. 
3 
-78 28 
-1 13 
-79 41 
- 5 
— 1 05 
-79 33 
-12 
s. by w. 
3 
— 78 28 
-1 29 
-79 57 
+ 11 
— 1 13 
-79 41 
— 2 
s. 
5 
-78 32 
— 1 31 
-80 03 
+ 17 
-1 14 
-79 46 
+ 1 
Means 
36 
— 79 46- a 
— 79 45 = a 
The mean of the observations in the table thus corrected is —7 9° 45'; the corre- 
sponding geographical position is —66° 04', and 203° 17' - 5, if we take as such the 
middle point of the geographical space in which the ship was detained from the 6th 
to the 16th of January. The inclination observed on the ice on the 16th of January, 
in lat. —65° 49', long. 202° 02', with needles whose poles were reversed, was -—79° 39'*5. 
We can derive no precise conclusion in regard to the value of d, from observations 
which are not identical in locality ; but the accordance of the results obtained on board 
and on the ice, in geographical positions so little different, is quite sufficient to show 
that the error involved by assuming d as unity must be, at the utmost, very in- 
considerable. 
The tables for the correction of the inclination in the Erebus have therefore been 
computed with the following values for the constants, viz. from New Zealand to the 
end of February i842, being the portion of the voyage in which the ship was in pro- 
