154
LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM.
Ship’s head
Disturbance towards the west.
Ship’s head
Disturbance towards the west.
by compass.
1840.
1841.
Mean.
by compass.
1840.
1841.
Mean.
N.
O /
+ 1 10
o /-0 26
+ 0 22
s.
o t
-0 49
o t
+ 0 43
o /
-0 03
n. by w.
+ 0 24
-1 14
-0 25
s. by e.
-0 01
+2 32
+ 1 15
N.N.W.
-0 40
-2 01
-1 20
S.S.E.
+ 0 38
+ 3 06
+ 1 52
n.w. by n.
— 1 54
—2 34
— 2 14
s.e. by s.
+ 1 12
+ 3 51
+ 2 32
N.W.
-2 10
-2 55
— 2 32
S.E.
+ 1 35
+ 4 34
+ 3 04
N.w. by w.
— 2 58
-3 13
-3 05
s.e. by e.
+ 2 35
+ 5 01
+ 3 48
W.N.W.
— 3 18
—3 51
—3 35
E.S.E.
+ 3 17
+ 4 45
+ 4 01
w. by n.
-3 39
-4 32
-4 06
e. by s.
+ 3 12
+ 5 21
+4 17
w.
—4 15
-4 59
-4 37
E.
+ 3 38
+ 5 07
+ 4 22
w. by s.
-4 13
— 4 56
-4 35
E. by n.
+ 3 54
+ 4 46
+ 4 20
w.s.w.
-4 27
-4 41
-4 34
E.N.E.
+ 3 30
+ 4 06
+ 3 48
s.w. by w.
-4 39
-4 19
-4 29
n.e. by e.
+ 3 21
+ 3 45
+ 3 33
s.w.
— 4 06
-3 40
-3 53
N.E.
+ 3 12
+ 3 08
+ 3 10
s.w. by s.
-3 36
-2 50
—3 13
n.e. by N.
+ 2 50
+ 2 39
+ 2 45
s.s.w.
-2 30
—2 15
—2 22
N.N.E.
+ 2 26
+ 1 30
+ 1 58
s. by w.
-1 39
-0 19
-0 59
N. by e.
+ 2 19
+ 0 38
+ 1 28
Employing the same formula as before, and forming equations from the observa-tions on the twenty eight points, being all the points excepting the north, south, eastand west, we obtain
10-1036 b = + 9-9673b — + -9865 ;
and from the sum of the thirty equations, including those at east and west, we have
+ 57-89 a = + 1-0439 + -537 b,
a —
1-0439 + -529757-89
= + -0272.
On the passage from Hobarton to the Antarctic Circle, the Expedition stopped atAuckland Island for the purpose of observing on the term day of November 1840.The Erebus was not swung at this station, but with the value of 0 observed on shore— 73° 10', and the declination observed on board whilst at anchor, with the ship’shead on the east and west points, and on the E.N.E. and W.N.W. points, we mayobtain a satisfactory value for a. On the supposition of the symmetrical distributionof the iron on either side of the longitudinal midship section, the deviation occasionedby it should be the same in amount, but with opposite signs, at east and west, andalso at E.N.E. and W.N.W.; the amount, however, being slightly different at eastand west from that at E.N.E. and W.N.W.
From the observations at east and west we have
4>’ = — 12° 52' at east, and ■»£' = — 22° 55' at west;. 4 / + V
4 = — 2 ^ = - 17° 53 -5, andi = i 5° 0l'-5 ; whence a = -0265.