e directions, in
order to make them unlike poles. The current is supposed to pass around
B, Fig. 60, in the direction taken by clock hands, while it passes
around A in an anti-clockwise direction. The inside ends, Sec. 123, of
the coils may be twisted together, or fastened under a screw-head. In
Fig. 60 one coil is shown to be a continuation of the other.

[Illustration: Fig. 60.]

APPARATUS 86.

[Illustration: Fig. 61.]

[Illustration: Fig. 62.]

_116. Electro-Magnet._ Fig. 61. Wind 6 layers of No. 24 or 25 insulated
copper wire around a 5/16 machine-bolt that is 2-1/2 in. long. Fig. 61
shows one method of holding the bolt solidly in an upright position, so
that magnetic figures can be easily made and the magnet studied. Two
nuts are used, the lower one being counter-sunk, so that the base will
stand flat upon the table. This bolt is shown without washers (Sec. 119),
and will do fairly well to show the action of electro-magnets. The ends
of the wire should always be left 5 or 6 in. long, and be led out to
binding-posts. The coil may be held in place, and its turns kept from
untwisting by coating it with paraffine. The base may be of any desired
size.

APPARATUS 87.

_117. Electro-Magnet Core._ Fig. 62. This shows another method of
fastening a bolt-core in an upright position. This is done without the
use of two nuts. A strip of tin, T, 1 in. wide, is punched and slipped
onto the 5/16 bolt before the nut is screwed on and the coil wound. This
is fastened to the base by screws, S. Washers, W, are here shown. (See
Sec. 119 for washers.)

APPARATUS 88.

_118. Bolt Electro-Magnets_ are easy to make, according to the
directions given, and they are, when finished, more like the regular
purchased magnets than any of the other forms described. With proper
batteries (App. 3, 4, etc.,) they can be used for a great variety of
purposes, as will be seen. There are many forms of bolts in the market,
but the ordinary "machine bolt," 5/16 in. in diameter, is best for our
purposes. The ones 2 and 2-1/2 in. long are used.

119. Washers or coil ends are used on the bolt magnets so that
considerable wire can be wound on closely and evenly. These are made out
of thick pasteboard, which cuts smoother if it has been soaked in melted
paraffine. Unless you know how, you will find it a hard job to make the
hole in the exact center of the washer. The method of easily making
washers is illustrated in Fig. 63.

First place a s