LIEUT. -GENEEAL SABINE ON TEEEESTEIAL MAGNETISM. 379 
the observation of deviation and horizontal intensity, it will in general be better to use 
it than the value of s ; n 23 ,' aU( J i + 2 ^ obtained from the observations of dip and total 
intensity. 
The observations for the 4 Erebus ’ at Hobarton treated in this way give 
3 ' sin + { - 3'+ 81' cos 25} cos £-14' sin 25 cos 2£, 
“ ‘ 001 c °s 25 + -0234 sin 2d cos £ + -004(1 +cos 2d) cos 2£. 
This is the formula from which the Tables used for correcting the dips and intensities 
observed in the 4 Erebus ’ have been computed. 
P.S. It may be convenient for persons who make use of the Admiralty Manual to 
have the expressions for L, M, N, P, Q, K, A', a, i, c, d in the notation of that work. 
E= 1 — a.) sin 25, 
M ■ = + 10 — c) + \{g + c) cos 25, 
N=— sin 25, 
P= \{Jc— 1 -{-?*.)— cos 25, 
Q= + \{g+c) sin 2d, 
E=+ixT)(l + cos25> 
This Memorandum. 
A' = 
Admiralty Manual. 
l+ff=A(l+ 2 )), 
c S3 
l + ffl~l+® cot ^ 
l+c 1-T) 
1 +a 1 +®’ 
C 
d 
9 
1 +a 
1+k 
1 -|- CL 
Before the ‘Erebus’ and ‘Terror’ sailed from Hobarton in November 1840 to 
commence the first year of the Survey, the deviations of the Declination, as shown by 
the Standard Compass in each ship, were very carefully observed; and the observations 
were repeated on the return to Hobarton at the conclusion of the first year’s Survey, in 
June 1841. The results are printed in Contributions No. V., those of the • Erebus ’ in 
page 154, and those of the ‘Terror’ in page 159. Tables for the correction of the 
Deviation m the different values of the Inclination, ’in the first and second years of the 
urvey, were computed from these observations, employing Mr. Archibald Smith’s 
MDCCCLXVIII. 3 G 
