156 
LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
s. 
S'. 
s. 
N.w. by N. 
— 2-12 
33 45 
31 33 
N.W. 
-2-07 
45 00 
42 53 
n.w. by w. 
— 2-42 
56 15 
53 33 
s.w. by w. 
— 3-52 
123 45 
119 53 
s.w. 
— 3*28 
135 00 
131 32 
s.w. by s. 
-2-38 
146 15 
143 37 
s.e. by s. 
+ 2-45 
213 45 
216 30 
S.E. 
+ 3-16 
225 00 
228 16 
s.e. by e. 
-f 3*47 
236 15 
240 02 
n.e. by e. 
+ 2-08 
303 45 
305 53 
N.E. 
+ 2*03 
315 00 
317 05 
n.e. by n. 
+ 1-27 
326 15 
327 42 
Employing these values of g' and <^in the formula 
cos £ sin — b cos sin <^+ a tan ® sin = 0, 
and eliminating a tan 6 sin we have 
57471 b — 5*6233 ; b = '9785. 
Collecting now in one view the values of a, we have as follows : — 
1. From the observations at Gillingham near Chatham a — + *0264 
2. From the observations at Hobarton a — + ‘0272 
3. From the observations at Auckland Island . . . a = + '0263 
4. From the observations in lat. — 68° 30', long. 176° 35' a = + "0267 
Mean. . . . +‘0267 
From this near accordance in the values of a, obtained in dips varying from + 69° 05' 
to — 83° 35', we are warranted in regarding the local attraction in the Erebus as due 
to induced magnetism ; and in employing the formulae derived from M. Poisson’s 
fundamental equations, which are based on the hypothesis of induced magnetism 
only, in computing corrections for the observations made on board that ship. 
For the value of b we have 
From the observations at Gillingham b = + *9874 
From the observations at Hobarton b — + '9865 
From the observations at Kerguelen Island . . . b = -f- *9785 
Mean . . . + -9841 
With these values of a and b, a table of double entry was formed, having for argu- 
ments £■' and 0 ; £*' being the compass direction of the ship’s head when an azimuth 
was observed, and 6 the inclination taken from the chart formed from the observa- 
tions of that element on board ship, corrected in the manner that will be shown 
hereafter ; the corrections for the ship’s local attraction in the general Table of Decli- 
nations observed in the Erebus have been taken from the Table thus formed. 
