ON THE MAGNETIC INTENSITY OF THE EARTH. 79 
of 138° in Siberia; and it is possible that a navigator sailing 
from the Pacific through Behring’s Strait, and passing the Bay 
of St. Lawrence where Admiral. Liitke observed 1°65, might 
proceed to the northward having the spaces included by the 
closed curves of 1:7 on either side of him. 
The space inclosed by the curve of 1°8 possesses a very high 
degree of magnetic interest, and is well deserving of being 
traversed by observations as frequent and as accurate as those 
of MM. Hansteen and Erman in Siberia. The greater part of 
it is in the British dominion, and over a considerable portion at 
least convenient means of locomotion are to be found. The 
British Association had but to express the wish that a magnetic 
survey of the British Islands should be made, and it was at 
once responded to by some of its ownmembers. ‘The present 
volume contains the record of the completion of that under- 
taking ; and it may be permitted to one of the contributors to 
that work to express a hope, that the attention of the Associa- 
tion may now be given to the British possessions abroad. 
In the extensive territory under British dominion in India, not 
a single determination has yet, I believe, been made of the 
magnetic intensity, and but few of either of the other pheno- 
mena. From the well-known zeal of the officers of the Indian 
service, a recommendation in the proper quarter would speedily 
cover that large portion of the earth’s surface with accurate 
magnetic determinations. But the Canadian quarter is of pro- 
minent interest; a correct delineation of the lines of variation, 
dip, and intensity in the space included by the curve of 1°8, or 
_ in even a portion of that space, would have a high value in 
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theoretical respects. 'The accomplishment of this service is 
not altogether beyond the compass of individual means, and 
needs not, like a southern voyage, await the success of an ap- 
plication to Government. It requires only for its proper ex- 
ecution, that it should be the principal object of the person 
undertaking it, and that he should be provided with adequate 
instruments. Were the wishes of the Association expressed in 
regard to Canada, as they were in regard to the British Is- 
lands, I have little doubt that they would soon be complied 
with by members of their own body*. 
* The ground which Capt. Back traversed in his journey in search of Capt. 
Ross in 1833 and 1834 is of great interest as regards the magnetic intensity ; 
and had that officer been furnished with suitable instruments, and had it ac- 
corded with his other objects to have made observations in the manner of MM. 
eensteen and Erman at every halting-place, his results might have possessed 
great value. 
The vibrations of the dipping-needle, which he employed to measure the in- 
