t into
play. George took a hand in the work, and while they were preparing the
metal for the little bar, said: "You spoke about a permanent magnet.
What other kinds of magnets are there?"

"Magnets are permanent or temporary. A permanent magnet is one in which
the electricity resides, or remains, as it does in the earth. A
temporary magnet is one which has magnetism imparted to it only while a
current of electricity is passing around it."

"How is the current made to pass around it?"

"By wrapping an insulated wire around it, and sending a current through
the wire. When that is done the same thing is done to the bar as the bar
of the permanent magnet exhibits. As soon, however, as the current
through the wire ceases, the bar is again demagnetized. That is, it
ceases to be a magnet."

"We have the small bars ready, Professor. What is the next step?"

"It must be hardened so as to make it a flinty steel. The harder the
better, so that it will preserve the magnetism imparted to it."

"Is that the better way to make the temporary magnet?"

"No; in that case the bar should be of the softest iron. Remember,
therefore, that for a permanent magnet, use the hardest steel, and for a
temporary one, the softest iron."

"Then as we want to make a permanent magnet, must we harden both of the
bars?"

"No; for our uses, one must be left soft, because on that we shall want
to wind some insulated wire to make a temporary magnet."

The small amount of wire which was on hand was then coated with a thin
layer of the ramie fiber, which was carefully wrapped around, so that
the different layers of wire could not touch each other. When this was
completed, a spool was constructed, which fitted over the little bar or
rod, because they were rounded off, and one end of the soft iron rod
extended out beyond the spool.

The opposite ends of the winding were then brought out and attached to
the terminal wires of the battery. A test showed that the magnet thus
made would readily pick up pieces of iron or steel. The Professor then
took the hardened steel rod, through which a small hole had been bored,
midway between its ends, and laying it down on the table, the projecting
end of the temporary magnet which projected from the spool was put into
contact with the hard steel rod, and slowly drawn along to the end. The
soft bar magnet was then raised up and again repeated, as shown in the
drawing (Fig. 20), where the dotted line (A) represents