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XIX. Discussion of the Magnetical Observations made by Captain Back, R.N. during 
his late Arctic Expedition. By S. Hunter Christie, Esq. M.A. F.R.S. 8$c. 
Received and Read June 2, 1836. 
Previous to Captain Back’s departure in 1833 with the expedition for the relief 
of Captain Ross, he consulted me respecting- the nature of the magnetical observa- 
tions which I considered it desirable should be made in the regions he was likely to 
visit. I was fully sensible that, however available the expedition on which he had so 
nobly volunteered might be made to the cause of science, its primary object, and 
that to which all others must give place, was the relief of our gallant countrymen, 
at that time considered to be in imminent danger of perishing in the inhospitable 
regions which their enterprising spirit had led them to explore. I therefore con- 
sidered it an object of the first importance, that whatever observations were to be 
made during the movements of the expedition should be so conducted as to cause 
as little delay as possible consistently with obtaining data for correct results, and 
also, that they should be made in the order of their importance. Compared with 
observations of the direction of the magnetic needle, both with reference to the me- 
ridian and to the vertical, other observations are of minor importance towards esta- 
blishing anything like a theory of terrestrial magnetism. Considering that observa- 
tions of the direction of the needle with reference to the meridian, though quite as 
important in a theoretical point of view as those with regard to the vertical, were 
necessarily called for in the conducting of the expedition, I, in the first instance, pointed 
out the observations which I considered necessary for determining the dip of the 
needle at the various stations where it might be practicable to make such observations ; 
and I left the less important ones for the determination of the relative intensities of 
the absolute force acting upon the needle, which required more care, attention and 
assistance, to be made or not, according to the circumstances under which the ex- 
pedition might be placed. Immediately on his return. Captain Back did me the 
favour to place all his magnetical observations at my disposal, and I feel that I should 
not do justice to the zeal and ability which that enterprising officer has displayed in 
the cause of science, if I did not, now that I have had leisure to reduce the observa- 
tions, lay an account of them before the Royal Society. 
I. Observations of the Dip of the Magnetic Needle. 
The instrument employed for determining the dip was a small but very accurate 
one, by Dollond, furnished with two rectangular needles, each three inches in length. 
mdcccxxxvi. 3 c 
