The Inclination or Dip of the Needle was first recorded by Robert
Norman, in a scarce book published in 1576 entitled _The New
Attractive; containing a short Discourse of the Magnet or Loadstone,
&c._
Columbus has not only the merit of being the first to discover _a
line without magnetic variation_, but also of having first excited a
taste for the study of terrestrial magnetism in Europe, by means of
his observations on the progressive increase of western declination in
receding from that line.
The first chart showing the variation of the compass,[48] or the
declination of the needle, based on the idea of employing curves drawn
through points of equal declination, is due to Halley, who is justly
entitled the father and founder of terrestrial magnetism. And it is
curious to find that in No. 195 of the _Philosophical Transactions_,
in 1683, Halley had previously expressed his belief that he has put it
past doubt that the globe of the earth is one great magnet, having four
magnetical poles or points of attraction, near each pole of the equator
two; and that in those parts of the world which lie near adjacent to
any one of those magnetical poles, the needle is chiefly governed
thereby, the nearest pole being always predominant over the more remote.
“To Halley” (says Sir John Herschel) “we owe the first appreciation
of the real complexity of the subject of magnetism. It is wonderful
indeed, and a striking proof of the penetration and sagacity of this
extraordinary man, that with his means of information he should
have been able to draw such conclusions, and to take so large and
comprehensive a view of the subject as he appears to have done.”
And, in our time, “the earth is a great magnet,” says Faraday: “its
power, according to Gauss, being equal to that which would be conferred
if every cubic yard of it contained six one-pound magnets; the sum of
the force is therefore equal to 8,464,000,000,000,000,000,000 such
magnets.”