L1EUT.-C0L0NEL SABINE ON TERRESTRIAL MAGNETISM. 
157 
In geographical positions, where the indication made a very near approxima- 
tion to — 90°, and when azimuths observed on the same day at places sufficiently 
near to each other included observations on the east and west points, or on points 
but little removed from them, on which the corrections for the deviation might have 
the same, or nearly the same, value, but with opposite signs, the inclination with 
which the corrections have been computed has been derived from the azimuths them- 
selves in preference to being taken from the chart. In such cases, and when a and b 
have been elsewhere satisfactorily determined for the ship, the amount of disturbance 
which her iron produces on the compass needle furnishes itself a measure of the 
inclination, exceeding in precision that of the dipping needle used on board. If the 
ship’s magnetism should have already conformed to the terrestrial dip, the inclination 
corresponding to the disturbance of the compass is that belonging to the geogra- 
phical position, and the ship herself, with merely her compass needle, would become 
in such rare situations an inclinometer of great delicacy. But if the change in the 
magnetism of the ship from that due to a former magnetic locality be not yet fully 
developed, the inclination thus furnished by the compass needle is on that account 
also preferable to that which might be taken from the chart, or to the dip observed 
with the dipping needle either on board or on shore, for the correction of other 
azimuths observed at the same time. Whenever the inclination used for the decli- 
nation corrections has been thus derived, a notice is annexed in its proper place in 
the general table. It may be useful to give an example, and I select for that purpose 
the observations on the afternoon of the 16th February 1841, when, from the amount 
of the declination (— 112° or — 113°), the Expedition had without doubt penetrated 
to the south of the latitude of the magnetic pole ; the particular observations are as 
follow : — 
Latitude. 
Longitude. 
Ship’s head. 
?'• 
Declination observed. 
■V- 
C* 1 
-76 35 
166 17 
e. by s. \ s. 
— (54 23 ; 
76 36 
166 17 
N.N.W i W. 
-136 19 
-76 36 
166 17 
W.N.W. 
— 150 04 
-76 36 
1 66 16 
N.w. by n. 
— 138 24 
-76 36 
166 16 
w. 
— 158 51 
-76 36 
1 66 16 
w. by s. \ s. 
— 156 58 
-76 36 
166 16 
s.w. A w. 
— 156 05 
-76 36 
166 17 
s.w. by n. 
-154 06 
-76 36 
166 17 
S.W. I s. 
— 142 54 
-76 37 
166 16 
E.N.E. 
- 67 01 
-76 37 
1 66 16 
e. by s. 
— 67 53 
-76 37 
166 16 
e. by s. 
— 66 32 
-76 37 
166 16 
E.S.E. 
— 73 45 
-76 37 
166 35 
s.e. by e. 
— 73 40 
From the observations at W., and E. by S., we have the approximate values of 
4 = ^ = — 113° 01'; o at W. = — 45° 50' ; tan & = whence 6= — 87° 52'. 
y 2 
