It is well not to wind to the extreme ends of the paper
insulations, but to leave a space of about 1/8-in. at each end of
the winding to prevent the wires of one layer slipping over the
ends of the paraffin
[Illustration: Induction Coil]
paper and coming in contact with the layer beneath, thus causing a
short circuit. The secondary winding should have at least a dozen
layers and should be carefully wound to prevent short circuiting.
In order to reduce the strength of the current a piece of brass
tubing, F, is pushed into the space, C, surrounding the core, or
if no brass tubing of the required size is on hand, roll a paper
tube, cover with 4 or 5 thicknesses of tinfoil and then wrap with
more paper, using glue to hold the tinfoil in place and to keep
the tube from unwinding. When the tube is pushed all the way in,
the current produced
[Illustration: Induction Coil]
will be almost unnoticeable, but when it is withdrawn the current
will be so strong that a person cannot let go the handles until
the coil is shut off. After the secondary coil is wound it should
be covered with stiff paper, and the whole coil, including the
wood ends, should then be enameled black.
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