e use of these switches, etc., will be shown in the
proper place. Their construction only will be given here.

APPARATUS 36.

_53. Cut-Out._ Fig. 22. Details. X, Y, and Z represent 3 binding-posts
like App. 42. These are fastened to a wooden base that is about 3 x 5 x
3/4. The ends of the wires shown come from and go to the other pieces of
apparatus. Q shows a stout wire or strip of 2 or 3 thicknesses of tin.
Suppose we have an apparatus, as, for example, an electric bell, which
we want to have ring when someone at a distance desires to call us. If
we use a telephone or telegraph instrument we shall want to cut the bell
out of the circuit as soon as we hear the call and are ready to talk.
Suppose the current comes to us through the wire, A, Fig. 22. It can
pass by the wire, C, through the bell and back to X. If we wanted simply
to have the bell ring, the current could pass directly from X into the
earth, or over a return wire back to the push-button at our friend's
house. If, however, we are to use some other instrument, by lifting the
end of Q out of X and pushing it into Y, the bell will be cut out, and
the current can pass on wherever we need it.

[Illustration: Fig. 22.]

APPARATUS 37.

_54. Cut-Out._ Fig. 23. The main features of this are like those of App.
36. The three binding-posts are like App. 46. Instead of a band of metal
to change connections, as Q in App. 36, a stout copper wire is used.
This can be easily changed from one of the upper binding-posts to the
other, thereby throwing in or cutting out any piece of apparatus joined
with the upper connectors.

[Illustration: Fig. 23.]

APPARATUS 38.

[Illustration: Fig. 24.]

_55. Switch._ Fig. 24. This simple switch has but one contact point, D,
which is a screw-head. This switch may be used anywhere in the circuit
by simply cutting the wire carrying the current, and joining the ends of
the wire to the binding-posts X and Y. The metal strip, E, is made of 2
or 3 thicknesses of tin. It is 5/8 in. wide and about 5 in. long, and
presses down upon D, when swung to the left, thus closing the circuit.
The short metal strips shown are 5/8 x 1-1/4 in. The upper strip is
joined to the end of E by a coiled copper wire, C W. (See App. 50.) If
the current enters by the wire, A, it will pass through C W, E, D and
out at B. The strip E is pivoted at F by a small screw. The base may be
3 or 4 x 5 x 7/8 in.

APPARATUS 39.

_56. Switch._ Fig. 25. By incre