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' ELECTRIC TELEGRAPHS 161

There are many forms of relays, and while that which is
described below is not of the type commonly used on tele-
graph lines, it has the advantage of being far more sensitive
than any instrument of the regular line relay type that the
average experimenter could build.

Make the magnets from one-quarter-inch stove-bolts,
and cut them off so that they will form a core about two and.

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IRON YOKE
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MAGNET SPOOL CONTACT LEVER.
FIG. 138. —Details of the Relay Parts.

 

 

 

 

one-quarter inches long. Fit each of the cores with two
fiber heads to hold the wire in place. Insulate the legs with
paper and wind each with about fifty layers of N o. 30 B. &
S. gauge single-cotton-covered magnet wire. The winding
space between the magnet’s heads should be one and one-
eighth inches.

The upper ends of the magnet cores should be allowed to
project about one-quarter of an inch beyond the fiber head.
The end of the core is filed flat, as shown in the illustration.

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