LIEUT. -COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
173 
§ 9. Observations of the Magnetic Inclination and Intensity made on board Her Ma- 
jesty's ship Erebus on the passage from Kerguelen Island to Van Diemen Island 
in July and August 1840. 
These observations were made with Mr. Fox’s apparatus, and with the same needle 
F which had been employed in the determinations made at sea on the passage from 
England to Kerguelen Island, discussed in § 5 and § 6 of these Contributions*. The 
inclinations at sea were observed with the face of the circle always to the east : the 
index correction for needle F in this position of the instrument has been derived by 
comparing similar observations made with it at the magnetic observatory at Kerguelen 
Island, with the results obtained at the same spot with other needles which had their 
poles reversed. These are contained in the following Table : — 
Observations of the Indication with needles whose poles were reversed, made at the 
Magnetic Observatory at Kerguelen Island, July 1840. 
1840. 
Hours. 
July 4. 
6 . 
6 . 
6 . 
6 . 
8 . 
9. 
9. 
10 . 
h m 
10 A.M. 
6 P.M. 
6 15 p.m. 
6 30 p.m. 
7 20 p.m. 
1 45 p.m. 
5 30 p.m. 
7 30 p.m. 
9 A.M. 
Needle. 
' 
C 1 
c 
C 1 
C 2 
C 2 
R 4 j 
R G 1 | 
R G 2 | 
R 10 
Poles. 
a direct. 
(i reversed. 
a — 69 
/3— 6 9 
a — 69 
0-69 
a -69 
0-70 
a -69 
0-6 9 
a — 69 
0-70 
a— 70 
0-70 
a — 69 
0-70 
a-69 
0-70 
a — 70 
0-70 
59-7 
58- 4 
59- 0 
50 2 
59-8 
01-6 
597 
48-7 
47-8 
01-0 
03-1 
02-0 
54-3 
03- 8 
57-7 
04- 0 
13-9 
08-9 
Mean. 
j -69 59-0 
-69 54-6 
-70 00-7 
| -69 54-2 
| —69 54-4 
-70 02-5 
Remarks. 
Needles belonging to H. M. S. Terror. 
'Obi 
servers. 
f Captain Crozier, 
[ Lieut. Kay. 
j -69 59-1 
| _70 00-8 
j -70 11-4 
Needles belonging to H. M. S. Erebus. 
Observer, Captain Ross. 
-69 59-6 
General Mean. 
The inclination observed with needle F at the same spot with the face of the circle 
towards the east was — 69° 57 ,- 9 ; whence the index correction is — l ,- 7- 
The intensity of the magnetic force was determined in this portion of the voyage, 
on every day that the weather permitted, by the angles of deflection caused by a de- 
flecting magnet. The observations were a continuation of the series of which the 
earlier portion is given in § 5 and § 6. The deflecting magnet employed was the 
deflector S. Tables are given, in the sections referred to, of the values of w' for this 
deflector corresponding to angles of deflection from 42° to 25°, derived from a com- 
parison with the deflections produced by weights. The increase of the terrestrial 
force, in the passage between Kerguelen and Van Diemen Islands, brought the angle 
* Philosophical Transactions, 1842, Art. II. 
2 A 2 
