160 
LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM. 
and for the other points 
c cos £ H - d tan Q = (cos £ + a tan 6) sec ’Q tan 0', 
and using the values of £ computed by means of the constants a and b already deter- 
mined, we have the following equations : 
N. + 1 -0000 c — 2-850 d — — 2*830 
N.N.W. + -9327 c - 2-850 d — — 2-845 
N.W. + -735 1 c — 2-850 d = — 2*868 
N.S.W.+ *4418 c — 2*850 d = - 2*848 
W. + *0761 c — 2*850 d = — 2*864 
W.S.W. — *3 139c- 2*850 d = — 2*889 
S.W. - *6617 c — 2*850 d— — 2*922 
S.S.W. — "9110 c — 2*850 d = — 2*888 
S. — 1-0000 c — 2*850 d = — 2*888 
S.S.E. — *91 10 c — 2*850 d— — 2*906 
S.E. — *6617 c — 2*850 d = — 2*902 
E.S.E. — *3139 c — 2*850 d = — 2*880 
E. + *0761 c — 2*850 d— — 2*858 
E.N.E. + *44 1 8 c — 2*850 d = — 2*862 
N.E. + *735 1 c — 2*850 d — — 2*845 
N.N.E. 4- *9327 c — 2*850 d = — 2*822 
Summing these equations, c is eliminated, and d — 
45-917 
45-604 
== 1*0069 ; and changing 
the signs in the equations from W. to E.S.E. inclusive and summing, we have 
+ •361 
C ~ 9*9924 
4- *0361. 
A similar series of observations made at Auckland Island on the passage from 
Hobarton to the Antarctic Circle, furnishes values of c and d differing but slightly from 
the preceding. The inclination observed on shore was — 73° 10'. 
Ship’s head by 
compass. 
Inclination 
observed. 
Ship’s head by 
compass. 
Inclination 
observed. 
N. 
-74 24 
s. 
— 72 00 
N.N.W. 
-74 34 
S.S.W. 
-72 17 
N.N.E. 
-74 09 
S.S.E. 
-72 05 
N.W. 
— 74 16 
S.W. 
— 72 36 
N.E. 
— 74 13 
S.E. 
— 72 38 
W.N.W. 
— 74 08 
W.S.W. 
-73 09 
E.N.E. 
— 73 43 
E.S.E. 
-73 02 
W. 
— 73 32 
E. 
— 73 26 
Treating these observations in a similar manner to those at Van Diemen Island, 
we obtain 
c = 4- *045 ; d — 4- 1*0039. 
Giving double weight to the observations at Hobarton, as representing a double 
series, we have c = 4" '639 ; and d = 4* 1’006. 
With these values of the constants in the formulae 
tan & — y tan 6 + cos ^ sin cosec from N.E to S.E., and from N.W. to S.W. 
tan (3 + cos ^ cos * 
tan & = C C "~g tan fl + cos ^ OT1 other P° intS ’ 
a table of double entrv v/as formed for the corrections of the observations of in- 
