North America in the year 1840, namely, Philadelphia, Washington, and Cambridge near Boston, in the United States; Toronto in Canada; and Sitka in Russian America; might all, with the exception of the last, be comprised in a circle of little over 200 miles radius; nor were any means at that time provided for attaining a knowledge of the absolute or relative values of the magnetical elements, or of their regular and irregular changes, in the northern parts of the British possessions; a region of peculiar interest, as comprising both the focus of maximum magnetic intensity in the northern hemisphere, and the point or pole of vertical dip. It was the principal purpose of the magnetic survey of British North America, authorized by the Government in 1841, and in part executed in the years 1843 and 1844, to supply the former deficiency; but with a view also to the latter, I was provided, in addition to other instruments with a complete set of transportable magnetometers, of the construction of Dr. Weber, as improved by Captain Riddell; and it was arranged with the authorities of the Hudson's Bay Company, that the excur. Sion of the first summer should terminate at Moose Factory on Hudson's Bay, where it was left optional with me to pass the whole of the ensuing winter, or to return in the course of it to Canada. The employment of these instruments in the magnetical term days.

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