first company to adopt this form of receiver as its standard type.
Their receiver is shown in cross-section in Fig. 52, and a photograph
of the same instrument partially disassembled is given in Fig. 53. The
most noticeable thing about the construction of this receiver is the
absence of permanent magnets. The entire working parts are contained
within the brass cup _1_, which serves not only as a container for the
magnet, but also as a seat for the diaphragm. This receiver is
therefore illustrative of the type mentioned above, wherein the
relation between the diaphragm and the pole pieces is not dependent
upon any connection through the shell.

[Illustration: Fig. 52. Automatic Electric Company Direct-Current
Receiver]

[Illustration: Fig. 53. Automatic Electric Company Direct-Current
Receiver]

The coil of this instrument consists of a single cylindrical spool
_2_, mounted on a cylindrical core. This bobbin lies within a soft
iron-punching _3_, the form of which is most clearly shown in Fig. 53,
and this punching affords a return path to the diaphragm for the
lines of force set up in the magnet core. Obviously a magnetizing
current passing through the winding of the coil will cause the end of
the core toward the diaphragm to be polarized, say positively, while
the end of the enclosing shell will be polarized in the other
polarity, negatively. Both poles of the magnet are therefore presented
to the diaphragm and the only air gap in the magnetic circuit is that
between the diaphragm and these poles. The magnetic circuit is
therefore one of great efficiency, since it consists almost entirely
of iron, the only air gap being that across which the attraction of