378 
MR. CHRISTIE ON THE MAGNETICAL OBSERVATIONS 
This instrument is more fully described in the Appendix to Captain Back’s Narrative. 
I have already stated that, in the mode of observing which I recommended to Captain 
Back, I had particular regard to the economy of time. Considering, therefore, that 
the operation of inverting the poles of the needle more than doubles the time required 
for observing without performing it, and, indeed, that it is one which can only be 
tolerated because generally necessary to counteract imperfections in the instrument 
employed, I proposed that, in general, this operation should be dispensed with. In 
order that the dip may be determined independently of this operation, it is necessary 
that the position of the centre of gravity of the needle employed, with reference to 
the axis of vibration, should be permanent, and that that position should be ascer- 
tained. Owing to the very short interval between the completion of the instruments 
and the departure of Captain Back, the observations made in London, from which, 
in conjunction with those to be made at the winter quarters of the expedition, I pro- 
posed determining this point, were not so satisfactory as might be desired ; and I 
have consequently been under the necessity of having recourse to the latter alone. It 
is therefore necessary that in giving an account of the observations for the dip of the 
needle I should commence with those at Fort Reliance, the winter station. 
Dip at Fort Reliance . — Of the two needles No. I. and No. II. belonging to the 
instrument, No. II. was reserved for determining the dip and intensity at the various 
stations, and was carefully preserved from all interference with its magnetic state ; 
but with No. I. the dip at Fort Reliance was determined by observations made with 
its poles direct and likewise inverted. In the following Table are given the means of 
five observations made with this needle in each position of the instrument, and the 
mean results of two sets of observations. 
Observations of the Dip at Fort Reliance with the Needle No. I. 
Date. 
1833. 
Oct. 10. 
1834. 
May 22. 
Time. 
h m 
f 1 1 15 A.M. 1 
\ 2 15 P.M. J 
J 3 10 p.m. 1 
j 8 20 p.m./ 
Poles of the needle direct. 
Poles of the needle reversed. 
Face of the needle 
Face of the needle 
to the face of instrument. 
reversed. 
■ the face of instrument. 
reversed. 
Therm. 
Means. 
Face of instrument 
Face of instrument 
i- acc of instrument 
Face of instrument 
East. 
West. 
East. 
West. 
East. 
West. 
East. 
West. 
o 
o / 
o / 
o / 
o / 
O 1 
o i 
o / 
O 1 
O 1 « 
41-25 
84 19-5 
84 17-5 
84 54 
84 25 
82 34-5 
GO 
CTi 
GO 
85 47-5 
82 12 
84 19 56 
47-0 
85 27 
83 27 
83 21 
85 00 
81 1-5 
83 44-5 
85 38-5 
00 
K) 
o 
83 42 30 
Mean dip at Fort Reliance 
QO 
In a paper “ On Improvements in the Instruments and Methods employed in de- 
termining the Direction and Intensity of the Terrestrial Magnetic Force,” published 
in the Philosophical Transactions for 1833, I have given the equations 
