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MISCELLANEOUS ELECTRICAL APPARATUS 377

three inches in diameter, make it six inches long and one
and one-half inches in diameter, etc.

The Primary consists of eight turns of No. IO B. & S.
gauge copper wire wound around a drum. The heads of
the drum are wooden rings, seven inches in diameter and
one—half inch thick. A circular hole four and one-half
inches in diameter is cut in the center of each of the heads.

The cross bars are two and one-
half inches long, three-quarters of
an inch thick and one-half of an ' .
inch wide. Six cross bars are re-
quired. They are spaced at equal
distances around the rings and
fastened by means of a brass screw
passing through the ring. When
the drum is completed it should .m“ .....
resemble a “ squirrel cage.” Fm. 319.—Details of the Cross

Small grooves are cut in the Bars whichfuppm the Pri‘

mary Winding.
cross bars to accommodate the
wire. The wires should pass around the drum in the form
of a spiral and be spaced about five—sixteenths of an inch
apart.

The ends of the wire should be fastened to binding-posts
mounted on the heads.

The Secondary is a single layer of No. 26 B. & S. silk- or
cotton-covered wire wound over a cardboard tube, twelve
inches long and three inches in diameter.

The tube should be dried in an oven and then given a

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