LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
163 
Deduction of the Constants in Her Majesty's Skip Terror . — For these we have, 
in the first place, the observations at Gillingham, in September 1839, as follows: 
6 = 69° 05'. 
Ship’s head 
by compass. 
Attraction 
towards 
the west. 
Ship’s head 
by compass. 
Attraction 
towards 
the west. 
Ship’s head 
by compass. 
Attraction 
towards 
the west. 
Ship’s head 
by compass. 
Attraction 
towards 
the west. 
N. 
N. by w. 
N.N.W. 
n.w. by n. 
N.W. 
n.w. by w. 
W.N.W. 
w. by n. 
+6-ii 
+ 1-35 
+ 2-31 
+ 3-9 
+ 3-58 
+ 4-39 
+ 5-8 
+ 5-35 
W. 
w. by s. 
w.s.w. 
s.w. by w. 
s.w. 
s.w. by s. 
s.s.w. 
s. by w. 
+ 5-55 
+ 5-17 
+ 4-39 
+ 3-50 
+ 3-8 
+ 2-24 
+ 1-38 
+ 0-55 
S. 
s. by e. 
S.S.E. 
s.e. by s. 
S.E. 
s.e. by e. 
E.S.E. 
e. by s. 
O 
— 0-8 
— 0-51 
— 1-42 
-2-30 
-3-9 
-3*40 
-4-34 
-4*57 
E. 
E. by N. 
E.N.E. 
n.e. by e. 
N.E. 
n.e. by n. 
N.N.E. 
N. by e. 
— 5*22 
-5-50 
— 5-22 
-4-27 
-3*37 
-2-37 
— 1-40 
-0-33 
We perceive by this Table that the masses of iron acting on the compass needle of 
the Terror were distributed, as in the Erebus, symmetrically, or very nearly so, 
on either side of the vertical plane passing through the longitudinal midship section. 
Using the formula 
cos <^sin (j' — h sin <fcos f' = a tan 0 sin fj, 
and forming equations for the several points, we have from the sum of those from 
N. by W. to W. by N., and from N. by E. to E. by N., 
— 4-4516 + 5-3295 h = + 23‘946 a ; 
and for the sum of the equations on the points from S. by W. to W. by S., and from 
S. by E. to E. by S., 
- 5-5092 + 47551 b = - 23’946 a, 
whence we derive b = + ‘987 7, and a — + -0339 ; or including the observations at 
east and west a — -0343. 
We have next to consider a similar series of observations made in the River Der- 
went, near Hobarton, in Van Diemen Island, on October 20th, 1840, soon after the 
first arrival of the Expedition at that station ; they were as follows : — 
Ship’s head 
by compass. 
Attraction 
towards 
the west. 
Ship’s head 
by compass. 
Attraction 
towards 
the west. 
Ship’s head 
by compass. 
Attraction 
towards 
the west. 
Ship’s head 
by compass. 
Attraction 
towards 
the west. 
N. 
n. by w. 
N.N.W. 
n.w. by N. 
N.W. 
N.w. by w. 
W.N.W. 
w. by N. 
+ 6 42-4 
-0 23*6 
-1 20-6 
-2 20-6 
— 3 25-6 
-3 56-6 
-4 01-6 
— 4 06*6 
w. 
w. by s. 
w.s.w. 
s.w. by w. 
s.w. 
s.w. by s. 
s.s.w. 
s. by w. 
-4 36-6 
— 4 44-6 
— 4 52-6 
-5 22*6 
-4 23-6 
—3 31-6 
-2 03-6 
— 1 37-6 
s. 
s. by e. 
S.S.E. 
s.e. by s. 
S.E. 
s.e. by e. 
E.S.E. 
e. by 
Of 
-0 11-6 
+ 0 52-4 
+ 1 56-4 
+ 2 38-4 
+ 3 29-4 
+ 4 00-4 
+ 4 43-4 
+ 4 28-4 
E. 
E. by N. 
E.N.E. 
n.e. by e. 
N.E. 
n.e. by N. 
N.N.E. 
n. by e. 
+ 4 24-4 
4-4 11-4 
+ 4 07-4 
4-3 27-4 
4-3 02-4 
4-2 37-4 
4-2 11-4 
4-1 26-4 
In the Terror, as in the Erebus, the disturbance had changed its sign in passing 
from the northern to the southern hemisphere: the symmetrical distribution of the 
MDCCCXLIII. 
Z 
