Year: 1878




though which II current ot electricity is
passing, he wound around apiece of ste,
~ soft IRON some c-llous things will hap.
pen. Ii the bar be soft iron 1t will be
made magnetic, and keep in that coudl-
ton as long as the current contisues to
pass round 1t, ana its end will then attract
and hold small bits ct iron, but drop them
when the battery is taken away. Ii the
bar be OF steel, intead rf soft iron, it will
be magnctizcd and attract iron Just AS
before, but, unlike the soft IRON bar, it
Will keep its magnets and attact the
iron even alter the battey is removed. It's
magnetism will be pc manent. Since,
however, electricity made the magnet, we
can, IN turn, make the magnet source of
electricity. Suppose the magne tzed steel
bar has attracted and is holding ON to q
piece OF iron. We Can now take the bat.
terry away and join the ends of the wire;
then, II the piece OF iron he pulled oft
ana stock on a4a n, Il current OF electricity
will run though the w.re eveVy time it is
done Electricity produced in this way is
called magneto-electricity, and the cur
rent in the wire is said to be an induced
electric current. IT. now, the wire from
one bar be extended tn distance, and
coIIed around another magnetized bar the
currents induced in it, by making and
breaking the contract of the piece of soft
iron with the first magnet, will simulta-
ncousIy affect the magnetism in the dis.
,ant magnet also. Though the magnets
Ue.


MILE OR A HUNDRED MILES APART.


The disturbance IN one is immendiate.
!y and equally manifested in the Other.
But what is still more remarkable these
induced currents may he sent though the
wire without the actual contact of the
soft iron with the steel bar. If this piece
OF iron is brought very near To one magnet
without touchingit, aud then withdrawn,
IN electrical thrill 9r wave is induced in
the wire, which is felt in tle distant
magnet, just rs ii the contact had been
actually made and broken. And so if We
play the piece of soft iron backwards
and forward before the magnet, no mat
ter how rapidly or slightly each motion is
felt as an electric pulse in the magnet at
The other end. To borrow IL metaphor
from life, it isas il the close approach and
quick oscillation of the piece Of soft iron
irettcd or tantalized the magnet and sent
II series electrical shudders though the
iron nerve. We have here the tunda-
mental principle of the telephone. No
galvanlc battery is employed to furnish an
electrical current, as in the case of the telr-
graph, but the currents in the wire are
produced by the motions 0f the piece of
soft iron near the magnet. Thus far we
have represented these motions in II very
Tade and coarse way, as if the piece Of iron
were vIbrated backward and forward by
the hand; but what we have really to
deal with is something infnitly more
delicate than this. The piece OF soft iron,
of which we have been speaking, rspre
sents what is called the diaphragm of the
telephone. which is thin, circular sheet
of iron, couple of inches in diameter,
held by its rim and adjusted so that its
center comes very close to the end of the
maguetzed bar And the motions which
now concern US are simply the vibrations
produced in this iron membrane by the
beats agnints it Of agltated air. Every
body knows that sounds are propagated
though the aerial medium by waves that
travel swiftly from their sources and that
we hear them because the waves strike
In rapid succession.


UPON THE DRUM OF THE EAR.


II is also well understood that these
wavca dlfer greatly in their Rates, depend
ing upon the mpidity of vibration in the
soundus body and, moreover, that they
are very complex, there being waves with.
IN waves of various orders in a single
tone. IL is the special complexily of
these waye-septems, in the different cases
that gives those pcculiar,es oi tone that
mark il.frrrnt musical instruments and
distln sh the voice Indifferent indiyid-
I"I1. These waves, start by 4 person