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Popular Mechanics Co.

"The Boy Mechanic: Volume 1 700 Things for Boys to Do"

One of the sheets of tin-foil is to
form one pole of the condenser, and the other sheet, which is
insulated from the first, forms the other pole or terminal. (This
condenser material is purchasable in long strips, ready for
assembling.)
The wiring diagram, Fig. 3, shows how the connections are made.
This method of connecting is suitable for all coils up to 1-1/2
in. spark, but for larger coil better results will be obtained by
using an independent type of interrupter, in which a separate
magnet is used to interrupt the circuit. Besides the magnetic
vibrators there are several other types, such as the mercury
dash-pot and rotary-commutator types, but these will become better
known to the amateur as he proceeds in his work and becomes more
experienced in coil operation.

** Combined Door Bell and Electric Alarm [114]
This device consists of a battery and bell connection to an alarm
clock which also acts as a door bell, the whole being mounted on a
board 18 in. long and 12 in. wide. Referring to the sketch
accompanying this article, the letters indicate as follows: A,
bell; B, battery ; C, switch; D, V-shaped copper strip; E, copper
lever with 1-in.


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