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I48 THE BOY ELECTRICIAN

place the clip on the key. Place the clock in such a posi-
tion that the two chains do not touch each other. Set the
clock. When the mechanical alarm goes ofl, the key will
revolve and twist the two chains, thus closing the electric
circuit and causing the bell to ring. The bell will ring until
the clamp is removed. The outfit can be attached to any
ordinary alarm clock.

An Annunciator-

Annunciators are often placed in bell and burglar alarm-
circuits to indicate where the button ringing the bell was
pushed, in case there
are several.

The separate in-
dicators used on an
annunciator are
called drops.

A drop may be
made from an elec-
tromagnet and
some brass strips,
etc.

The frame is cut
I from heavy sheet-
brass and shaped as shown in Figures 128 and 129.

The drop bar is a strip of metal which is pivoted on the
frame at its lower end and has the upper, end turned up to
receive a numeral or letter.

 

FIG. 128. — An Annunciator Drop.

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