CXIX
tions causes when approaching the pole of
the magnetic rod (N) an induced current
and whilst retreating its contrary current.
In consequence of this the magnetic rod at
the station B (M′) will be now strengthened,
then weakened, hence plate B' now attract
ed, then repulsed. This way the plate B′
makes as many vibrations as the plate B
and in doing so must produce the same
sound (word), which was spoken and it will
be heard in the mouthpiece at T′. The
first Telephone was constructed by Reis in
Germany 1862, but it was improved by
Graham Bell, Professor in Boston.
Remark I. In comparing galvanism with
frictional electricity it is obvious that both forces
are indentical, only that the electric machine pro
duces a greater tension, a galvanic battery a greater
quantity of electricity (the electric spark of a Ley
den jar smashes a piece of wood into pieces, but
lasts only for a moment; the electricity of a gal
vanic current breaks scarcely through the dry skin
of a finger, but it lasts as long as the wires are
closed). Very properly the electric machine was
compared with a waterless spring of high descent,
whilst the galvanic current is comparable to a
spring abounding in water, but of low descent. —
Carry out this comparison!
Remark 2. The effect of an electric current depends upon the quan
tity of electricity, which passes in a given time through the wire. The
quantity is the greater the less resistance the current has to overcome (by
good wires and good elements) and the stronger the electromotive force.
If P the quantity of electricity, W the resistance and E the electromotive
force, P = E/W. This law was discovered by Ohm (in Erlangen) 1827.
