diameter and depth, in a piece of
wood, and place 2 or 3 drops of mercury in this. The ends of wires
dipped in this will be electrically connected.

APPARATUS 50.

[Illustration: Fig. 34.]

_68. Connector._ Fig. 34. This shows how a wire may be fastened to one
end of a short strip of tin. At the other end of the strip a slot is
cut. This may straddle the body of a screw, or when left plain may be
used to slip between the two metal strips shown in App. 43.

APPARATUS 51.

_69. Binding-Post._ Fig. 35. The ends of two or more wires may be
quickly joined electrically by placing them between the nuts of a short
bolt. By using 3 nuts the bolt will more easily connect a large number
of wires.

[Illustration: Fig. 35.]

_Make Additional Notes and Sketches Here._

CHAPTER VI.

PERMANENT MAGNETS.

_70. Permanent Magnets_ may be made in many ways and from many different
kinds of steel. The steel used for needles, watch and clock springs,
files, cutting tools, etc., is generally of good quality, and it is
already hard enough to retain magnetism. (See Retentivity in text-book.)

APPARATUS 52.

_71. Bar Magnet._ A straight magnet is called a bar magnet. Magnetize a
sewing-needle. For some experiments a needle-magnet, as we may call it,
is better than a large magnet.

APPARATUS 53.

_72. Bar Magnet._ A harness-needle, which is thicker and stronger than a
sewing-needle, makes an excellent bar magnet.

APPARATUS 54.

_73. Bar Magnet._ For long slim magnets use a knitting-needle. Some
knitting-pins, as they are sometimes called, break off short when bent,
but most of them will bend considerably before breaking. These slim
magnets are excellent for the study of Consequent Poles. (See
text-book.)

APPARATUS 55.

_74. Flexible Bar Magnets._ It is often necessary to have flexible
magnets so that they may be bent into different shapes. These may be
made from watch or clock springs, as such steel, called spring steel,
will straighten out again as soon as the pressure is removed from it.
Corset steels, dress steels, hack-saw blades, etc., make good thin
flexible bar magnets.

APPARATUS 56.

_75. Strong Bar Magnets_ may be made from flat files. The handle end may
be broken off so that the two ends of the file shall be nearly alike in
size. These should be magnetized upon an electro-magnet.

APPARATUS 57.

_76. Compound Bar Magnets_ are made by first magnetizing several thin
pieces of steel