LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
107 
Elements of Calculation of the Intensity Observations. 
1 . With Weights. — The observations of the intensity of the magnetic force, during 
the period now under consideration, were made in both ships with Mr. Fox’s appa- 
ratus ; those in the Erebus with the same circle which had been used in the previous 
voyage, and those in the Terror with a circle of the same size as that of the Erebus, 
being the property of Captain Crozier, and received by him at Van Diemen Island. 
The needle employed to show the angles of deflection in the Erebus, marked R. F. 5, 
was not the same which had been used for that purpose in the voyage of 1840-1841, 
namely, R. F. 4, which now in its turn was used as a deflector. The weights employed 
in deflecting the intensity needle were 1, 2, 3, 4, 5 and 6 grains: the angles of de- 
flection obtained with one grain were however too small to yield results of the same 
satisfactory nature as those derived from the weights from two to six grains, and I 
have not therefore taken them into the account. The mounted needle in the Terror 
was marked F. C. B., a spare needle C being used as a deflector, in addition to the 
deflecting magnets belonging to the apparatus. The weights were 1, 1^, 2, 2^, 3 
and 3| grains. 
At Hobarton we have the deflections occasioned by the constant weights on the 
needle of the Erebus, April 1841, as follows : — 
Deflection. Therm. Deflection. Therm. 
grs. 
o / 
O 
grs. 
O / 
O 
r 2 
13 02-8 
60 
r 2 
13 14-5 
60 
3 
19 37'2 
60 
3 
19 55 5 
60 
Face East.< 
4 
26 477 
60 Face West.< 
4 
27 027 
58 
5 
34 23-5 
60 
5 
34 51*5 
58 
_ 6 
42 557 
61 
.6 
43 07-3 
58 
and in the needle of the Terror 
as follows : — 
Deflection. Therm. 
Deflection. 
Therm. 
grs. 
O / 
O 
grs. 
O / 
O 
1 
12 11-9 
60 
"1 
11 42-0 
60 
18 29-4 
60 
H 
17 52 6 
60 
2 
25 137 
60 _ 
2 
24 15-6 
60 
Face East.< 
Face West.< 
2 * 
31 430 
60 
ol 
31 007 
60 
3 
39 02-3 
60 
3 
38 42-3 
60 
Ql 
L<5 2 
46 5D3 
60 
3! 
L 0 2 
46 06'3 
60 
At Sydney, in July 1841, the deflections with the same weights were — 
Erebus. Terror. 
Deflection. 
Ther. 
Deflection. 
Ther. 
Deflection. 
Ther. 
Deflection. 
Ther. 
grs. 
O / 
O 
grs. 
O / 
O 
g rs - 0 
1 
O 
gr s - 0 
/ 
O 
"2 
13 57-4 
56 
"2 
14 32 6 
64 
"1 13 
CO 
60 
0 
60 
M 12 
44-1 
60 
3 
21 137 
55 
cn 
CD 
3 
21 514 
63 
U 20 
02-0 
60 
4-J 
H 19 
03-3 
60 
4 
29 09*2 
55 
£ 
< 
4 
29 32T 
64 
ccS 
w 
2 27 007 
60 
02 
CD 
£ 
2 26 
01-2 
60 
5 
37 43-3 
55 
0 
G$ 
5 
37 38-9 
63 
0 ) ^ 
o 
a 
2* 34 
252 
60 
0 
H 33 
177 
60 
-6 
46 517 
55 
-6 
47 32*4 
63 
& 
3 42 
06-9 
60 
3 41 
35*2 
60 
• 
_3± 51 
13-5 
60 
51 
02-1 
60 
