Miller, Kempster Blanchard, 1870-1933 · New York : McGraw publishing company · leaf 557
the matter of supervisory relays, one of the firstof these to be developed is of the type shown in Fig. 386, this typehaving been widely used in Bell exchanges. The coil, h, of this relay was in the earlier types enclosed in a heavyiron shell, the armature, d, serving when attracted to…
Telephone
Internet Archive · Cornell University Library · Public Domain Mark 1.0. Free to use for anything.
