, and to all in
which the receiver, transmitter, and hook are provided with a standard
of their own to enable them to rest on any flat surface, such as a
desk or table, as _desk telephones_. These latter are also referred to
as portable telephones and as portable desk telephones.

In general, magneto or local battery telephones differ from
common-battery telephones in their component parts, the difference
residing principally in the fact that the magneto telephone always has
a magneto generator and usually a local battery, while the
common-battery telephone has no local source of current whatever. On
the other hand, the differences between wall telephones and desk
telephones are principally structural, and obviously either of these
types of telephones may be for common-battery or magneto work. The
same component parts go to make up a desk telephone as a wall
telephone, provided the two instruments are adapted for the same class
of service, but the difference between the two lies in the structural
features by which these same parts are associated with each other and
protected from exposure.

[Illustration: Fig. 142. Magneto Wall Set]

[Illustration: Fig. 143. Magneto Wall Set]

Magneto-Telephone Sets. _Wall._ In Fig. 142 is shown a familiar type
of wall set. The containing box includes within it all of the working
parts of the apparatus except that which is necessarily left outside
in order to be within the reach of the user. Fig. 143 shows the same
set with the door open. This gives a good idea of the ordinary
arrangement of the apparatus within. It is seen that the polarized
bell or ringer has its working parts mounted on the inside of the door
or cover of the box, the tapper projecting through so as to play
between the gongs on the outside. Likewise the transmitter arm, which
supports the transmitter and allows its adjustment up and down to
accommodate itself to the height of the user, is mounted on the front
of the door, and the conductors leading to it may be seen fastened to
the rear of the door in Fig. 143.

In some wall sets the wires leading to the bell and transmitter are
connected to the wiring of the rest of the set through the hinges of
the door, thus allowing the door to be opened and closed repeatedly
without breaking off the wires. In order to always insure positive
electrical contact between the stationary and movable parts of the
hinge a small wire is wound around the hinge pin, one end being
sol