426 
GENERAL SIR EDWARD SABINE ON TERRESTRIAL MAGNETISM. 
has been assigned to Magnetical Observations in the successive Polar Voyages, and by 
the assiduous labours of British Naval and Military Officers, and of the Magneticians of 
the United States, acting in concert with the operations of the Coast Survey. The 
earliest authoritative knowledge we possess of the magnetical state of the North- Ame- 
rican Continent was contained in the same communication from Halley to the Boyal 
Society in 1683 to which reference has already been made. In that paper, the Geogra- 
phical Position of the “ North- American Magnetic Pole ” is stated to be in “ a meridian 
corresponding with the middle of California,” and “about 15° from the North Pole of 
the Globe.” We have, indeed, no assured knowledge as to whether the Geographical 
Position thus indicated was designed by Halley to refer to the locality characterized by 
“ 90° of Inclination,” or to that of the “ Maximum of Force,” — the distinction between 
these two localities being well known to Halley, as it was, in fact, established by himself. 
Our recent researches place the approximate localities of these points, in 1842 ‘5, — that 
of the maximum of Inclination in 70° N. Latitude and 263° E. Longitude ; whilst for 
the Maximum of Force we have the Latitude 53° N. and Longitude 268° E., — both 
localities being to the East, and a little to the South, of the Geographical Position which 
Halley assigned to the Magnetic Pole in 1683. Admitting the probability, which 
appears to be generally recognized and acceded to, that the Easterly Progression termi- 
nated at an Epoch nearly coinciding with that of the Maps and Tables of the present 
memoir, viz. 1842 - 5, such probability may seem to render the present occasion a parti- 
cularly suitable one for subjoining a few “ Groups ” of Results (as proposed in a previous 
page, p. 356) for convenient comparison with the Phenomena which maybe observed at 
future periods. 
