Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1872 Excerpt: ...the needle at Paris was a year or two later of leaving the due north, it turned at least a year, and, according to some reckonings, four years, earlier than at London from the point of maximum westerly declination. The latter circumstance so far accords with the easterly longitude of Paris: the former was an apparent anomaly, but meets partially with its solution now. (22.) In regard to the dip it is at once evident that the deflection towards the centre would cause the needle to be vertical at a slightly lower latitude than the real pole of the axis of the nucleus, and accounts for its being observed in latitude 70 5', instead of 71 30' north. In regard to the very perceptible and gradual diminution of the deflection after passing the quadrature which is shown in the last column of the Table, I think it is to be attributed to the influence of the south magnetic pole upon the needle becoming gradually more sensible. For up to near 80 of the secular revolution, the magnetic latitude of London was higher than its geographical latitude; but then it became equal; and since that time lower; and is still gradually becoming lower, as the north magnetio pole is steadily moving farther away, while at the same time the angular horizontal declination, and still more the inflection, are becoming less. Whether this increasing influence of the south magnetic ray may by and by, when the north magnetic pole approaches its extreme of distance from us, be sufficient to do more than counterbalance the central deflection, so as even to diminish the dip below what I have in the Table indicated as the minimum of the direct angle to the north pole of the nucleus, time and observation will show. But the fact that it is not yet equal to it, shows that no material error has resulted...
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