American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 593
CHICAGO POLICE PATROL BOX. 482 AMERICAN TELEGRAPHY. Special signals are transmitted by the police officer, or others having access to theboxes, by moving the pointer p. Fig. 359, to the designated point on the dial; which FIG. 360.
Telegraph
Internet Archive · Library of Congress · Public Domain Mark 1.0. Free to use for anything.
