Bibliographical history of electricity & magnetism, chronologically arranged
History
Bibliographical history of electricity & magnetism, chronologically arranged
Electricity -- History; Electricity -- History -- Bibliography; Magnetism -- History; Magnetism -- History -- Bibliography; Science, Medieval
“Electrics attract all things save flame and objects aflame, and
thinnest air ... for it is plain that the effluvia are consumed
by flame and igneous heat ... yet they draw to themselves the
smoke from an extinguished candle; and, the lighter the smoke
becomes as it ascends, the less strongly is it attracted, for
substances that are too rare do not suffer attraction.”
This Chapter II ends with the following explanation of the difference
between electric and magnetic bodies, viz. all magnetic bodies
come together by their joint forces (mutual strength); electric
bodies attract the electric only, and the body attracted undergoes
no modification through its own native force, but is drawn freely
under impulsion in the ratio of its matter (composition). Bodies
are attracted to electrics in a right line toward the centre of
electricity: a loadstone approaches another loadstone on a line
perpendicular to the circumference only at the poles, elsewhere
obliquely and transversely, and adheres at the same angles. The
electric motion is the motion of conservation of matter; the magnetic
is that of arrangement and order. The matter of the earth’s globe is
brought together and held together by itself electrically. The earth’s
globe is directed and revolves magnetically; it both coheres, and, to
the end it may be solid, it is in its interior fast joined.
Of the other interesting chapters in this Book II, attention is called
more particularly to:
Chap. IV. “Of the strength of a loadstone and its form: the
cause of coition.” The magnetic nature is proper to the earth
and is implanted in all its real parts ... there is in the
earth a magnetic strength or energy (_vigour_) of its own ...
thus we have to treat of the earth, which is a magnetic body,
a loadstone. An iron rod held in the hand is magnetized in the
end where it is grasped and the magnetic force travels to the
other extremity, not along the surface only but through the
inside, through the middle.... Iron instantly receives from
the loadstone verticity and natural conformity to it, being
absolutely metamorphosed into a perfect magnet. As soon as it
comes within the loadstone’s sphere of influence it changes
instantly and has its form renewed, which before was dormant and
inert, but now is quick and active.
Chaps. VI and XXVII illustrate the _Orbis Virtutis_ (Orb of
Virtue, or the magnetic atmosphere surrounding both earth
and loadstone alike), showing how the earth and loadstone
conform magnetic movements, the centre of the magnetic forces
of the earth being the earth’s centre and in the terrella the
terrella’s centre. All loadstones alike, whether spherical or
oblong, have the selfsame mode of turning to the poles of the
world ... whatever the shape, verticity is present and there are
poles.
Public-domain text, read in full here on John Shaqi.
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