nothing in common with the dynamo-electric generator, except that in
both something turns upon an axis as a grindstone or the barrel of
a barrel-organ may do. 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.

3. The third principle to be borne in mind is that to do work of any
kind, whether mechanical or electrical, requires the expenditure of
energy to a certain amount. The steam engine cannot work without its
coal, nor the laborer without his food; nor will a flame go on burning
without its fuel of some kind or other. Neither can an electric current
go on flowing, nor an electric light keep on shedding forth its beams,