_CHAP. I._
ON THE GLOBE OF THE EARTH, THE
_great magnet_.
Hitherto our subject hath been the loadstone and things magnetical: how
they conspire together, and are acted upon, how they conform themselves to
the terrella and to the earth. Now must we consider separately the globe
itself of the earth. Those experiments which have been proved by means of
the terrella, how magnetick things conform themselves to the terrella, are
all or at least the principal and most important of them, displayed by
means of the earth's Body: And to the earth things magnetical are in all
respects associate. First, as in the terrella the æquator, meridians,
parallels, axis, poles are natural boundaries, as numerous experiments make
plain: So also in the earth these boundaries are natural, not mathematical
only (as all before us used to suppose). These boundaries the same
experiments display and establish in both cases alike, in the earth no less
than in the terrella. Just as on the periphery of a terrella a loadstone or
a magnetick piece of iron is directed to its proper pole: so on the earth's
surface are there turnings-about, peculiar, manifest, and constant on
either side of the æquator. Iron is indued with verticity by being extended
toward a pole of the earth, just as toward a pole of the terrella: By its
being placed down also, and cooling toward the earth's pole after the
pristine verticity has {212} been annulled by fire, it acquires new
verticity, conformable to its position earthward. Iron rods also, when
placed some considerable time toward the poles, acquire verticity merely by
regarding the earth; just as the same rods, if placed toward the pole of a
loadstone, even without touching it, receive polar virtue. There is no
magnetick body that in any way runs to the terrella which does not also
wait upon the earth. As a loadstone is stronger at one end on one side or
other[240] of its æquator: so is the same property displayed by a small
terrella upon the surface of a larger terrella. According to the variety
and artistick skill in the rubbing of the magnetick iron upon the terrella,
so do the magnetick things perform their function more efficiently or more
feebly. In motions toward the earth's body, as toward the terrella a
variation is displayed due to the unlikeness, inequality, and imperfection
of its eminences: So every variation of the versorium or mariners' compass,
everywhere by land or by sea, which thing has so sorely disturbed men's
minds, is discerned and recognized as due to the same causes. The magnetick
dip (which is the wonderful turning of magnetick things to the body of the
terrella) in systematick course, is seen in clearer light to be the same
thing upon the earth. And that single experiment, by a wonderful
indication, as with a finger, proclaims the grand magnetick nature of the
earth to be innate and diffused through all her inward parts. A magnetick
vigour exists then in the earth just as in the terrella, which is a part of
the earth, homogenic in nature with it, but rounded by Art, so as to
correspond with the earth's globous shape and in order that in the chief
experiments it might accord with the globe of the earth.
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