The mirror. (Stillwater, Minn.) 1894-1925, 1899-06-22
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creased in one of the two remaining
ways; but when the external resistance
is very great, as in the case OF the
human body, in which it is about three
thousand ohms, the gain secured by en-.
larging the plates and lessening the
distance between them, is but trit1ing,
and the current-strength must there.
fore be increased by multiplying the
number of cells. When the external
resistance is slight, as in the galvano-
cautery, in which the current has only
to render a piece of wire in cOndes-
cent-the internal resistance becomes
highly mportant-and much is gained
by reducing it to minimum. 1t fol-
lows, therefore, that battery designed
for such purpose should consist of
few small cells, with large plates placed
very near one another. The same prin-
ciples likewise apply to the construction
of batteries, intended for electrolytic
work. Of the accessories to the gal
vanic battery, the most important, are
the galvano- meter, rheostat and elec-
trodes. A galvano- meter is an instru.
ment for measuring the current
strength.
A rheOstat. or resistance coil, is an
appliance for placing in the circuit,
known resistance; by it the external
resistance can be increased to any ex-
tent and kept uniform.
Electrodes are appliances, placed at
the pole-ends, so that the current can
be conveniently transferred to the body.
Faradism, or induced electricity
This manifestation of electrical force
depends upon the power which a gal
vanic current possesses. While passing
one conductor, of inducing momentarily
current in an overlying conductor.
The induced current is instantaneous,
and appears only at the making and
braking of the galvanic current. More
over, it flows in direction opposite to
that of the galvanic current, when the
latter is made, and in the same direct
ion, when it is broken. By rapidly
making and braking the primary cur
rent, powerful to-and-fro current is
induced in the overlying conductor. A
faractic battery consists of cell for
generating the galvanic current;
primary coil, consisting of few turns
of coarse insulated wire, enclosing a
coil of soft iron, secondary coil, COM
posed of many turns, of very fine wire,
surrounding the primary coil, but not
touching it, and mechanical device
for slowly or rapidly making or brak-
ing the current in the primary circuit.
The current derived from the pri-
mary coil is termed the primary cur
rent. Like the galvanic, it flows in one
direction, and affords positive and
negative pole. 1t differs, however, from
the galvanic current in being reinforced
by turns of the coil.
The current derived from the Sec
ondary coil is termed the secondary
current, and, since it is ever changing
the direction of its flow, it cannot fur
nish negative and positive poles.
Physiological action of electricity
When strange, uninterrupted current
is applied to the body, it produces at
the points of contact severe burning
pain, redness, and finally under the
negative pole visication. These phe-
nomena are the result of electrolytic
changes induced by the current. Mus
cular contraction results from the ap-
plication of the galvanic current only
during the opening and closing of the
circuit When the negative pole or
cathode is placed over the nerve sup
plying muscle, and the positive pole,
or anode, over some Indifferent point,
as the sternum, a contraction of the
muscle occurs on closing the circuit;
but with currents of ordinary strength