used by the public, that the necessary acts which a person must
perform in order to use the device must, as far as possible, follow as
a natural result from some other act which it is perfectly obvious to
the user that he must perform. So in the case of the switch hook, the
user of a telephone knows that he must take the receiver from its
normal support and hold it to his ear; and likewise, when he is
through with it, that he must dispose of it by hanging it upon a
support obviously provided for that purpose.

In its usual form a forked hook is provided for supporting the
receiver in a convenient place. This hook is at the free end of a
pivoted lever, which is normally pressed upward by a spring when the
receiver is not supported on it. When, however, the receiver is
supported on it, the lever is depressed by its weight. The motion of
the lever is mechanically imparted to the members of the switch
proper, the contacts of which are usually enclosed so as to be out of
reach of the user. This switch is so arranged that when the hook is
depressed the circuits are held in such condition that the talking
apparatus will be cut out, the battery circuit opened, and the
signaling apparatus connected with the line. On the other hand, when
the hook is in its raised position, the signaling apparatus is cut
out, the talking apparatus switched into proper working relation with
the line, and the battery circuit closed through the transmitter.

In the so-called common-battery telephones, where no magneto generator
or local battery is included in the equipment at the subscriber's
station, the mere raising of the hook serves another important
function. It acts, not only to complete the circuit through the
substation talking apparatus, but, by virtue of the closure of the
line circuit, permits a current to flow over the line from the