In the modern "dynamo" we cannot help having
friction at the bearings and contact pieces, it is true, but there
should be no other friction. The moving coils of wire or "armatures"
should rotate freely without touching the iron pole-pieces of the fixed
portion of the machine. In fact friction would be fatal to the action of
the "dynamo." How then does it act? We will proceed to explain without
further delay. There are, however, three fundamental principles to be
borne in mind if we would follow the explanation clearly from step to
step, and these three principles must be laid down at the very outset.
1. The first principle is that the existence of the energy of electric
currents, and also the energy of magnetic attractions, must be sought
for not so much _in the wire_ that carries the current, or _in the bar_
of steel or iron that we call a magnet, as _in the space that surrounds_
the wire or the bar.
2. The second fundamental principle is that the electric current is, in
one sense, quite as much a _magnetic_ fact as an electrical fact; and
that the wire which carries a current through it has magnetic properties
(so long as the current flows) and can attract bits of iron to itself as
a steel magnet does.
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