താൾ:CiXIV132a.pdf/428

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CXVI

§ 293. 7) Electromagnetism. It was Oersted who in
the year 1820 discovered that electrical currents tend to set the
magnetic needle at right angles to their own direction, and it is
Ampère's rule, that the north-pole of the needle is always de
flected towards the left of the current, a short time after
that Schweigger in Germany discovered the Galvanometer or
Multiplier, a very delicate instrument by which the existence,
direction and intensity of currents may be determined. 445.
(Comp. No. 110.) The wire of the galvanic battery is led in
many turnings above and below the needle.

§ 294. Bars of soft iron under the influence of a voltaic
current become magnets and are called Electromagnets; they
have the horse shoe-shape; a copper wire, covered with silk or
cotton, is rolled several times round them and connects them
with the voltaic battery. 446.

§ 295. Parallel electric currents of the same direction attract
each other, those of different direction repulse one another,
crossed currents, if not prevented, will appear as parallel cur
rents of the same direction.

§ 296. 8) Induction by currents. In a similar way, in
which a magnet produces in iron magnetism, an electric
current will call forth an electric current in a neighbouring con
ductor; this second current will be at the moment, in which it
comes into existence, contrary to the original current, at the
moment, in which it ceases, it will be of the same kind. These
secondary currents, lasting only for a moment, are called in
duced currents.

This induced current is in general used for producing phy
siological effects, because this momentary shock suits very well
to agitate the human body.

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