ne of these magnets is clamped to the south pole of the other, so
that in reality a horseshoe magnet is formed. At their lower ends,
these two permanent magnets are clamped against the soft iron pole
pieces _6-6_, a threaded block _7_ also being clamped rigidly between
these pole pieces at this point. On the ends of the pole pieces the
bobbins are wound. The whole magnet structure is secured within the
shell _1_ by means of a screw thread on the block _7_ which engages a
corresponding internal screw thread in the shell _1_. As a result of
this construction the whole magnet structure is bound rigidly to the
shell structure at a point close to the diaphragm, comparatively
speaking, and as a result of this close coupling, the relation between
the diaphragm and the pole piece is very much more rigid and
substantial than in the case where the magnet structure and the shell
were secured together at the end farthest removed from the diaphragm.

[Illustration: Fig. 50. Western Electric Receiver]

Although this receiver shown in Fig. 50 is the standard in use by the
Bell companies throughout this country, its numbers running well into
the millions, it cannot be said to be a strictly modern receiver,
because of at least one rather antiquated feature. The binding posts,
by which the circuit conductors are led to the coils of this
instrument, are mounted on the outside of the receiver shell, as
indicated, and are thus subject to danger of mechanical injury and
they are also exposed to the touch of the user, so that he may, in
case of the wires being charged to an abnormal potential, receive a
shock. Probably a more serious feature than either one of these is
that the terminals of the flexible cords which attach to these binding
posts are attached outside of the receiver shell, and are therefore
exposed to the wear and tear of use, rather than being protected as
they should be within the shell. Notwithstanding this undesirable
feature, this receiver is a very efficient one and is excellently
constructed.

[Illustration: Fig. 51. Kellogg Receiver]

Kellogg Receiver. In Fig. 51 is shown a bi-polar receiver with
internal or concealed binding posts. This particular receiver is
typical of a large number of similar kinds and is manufactured by the
Kellogg Switchboard and Supply Company. Two straight permanently
magnetized bar magnets _1-1_ are clamped together at their opposite
ends so as to form a horseshoe magnet. At the end opposit