ositively, 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
the diaphragm is to take place.

The action of this receiver will be understood when it is stated that
in common-battery practice, as will be shown in later chapters, a
steady current flows over the line for energizing the transmitter. On
this current is superposed the incoming voice currents from a distant
station. The steady current flowing in the line will, in the case of
this receiver, pass through the magnet winding and establish a normal
magnetic field in the same way as if a permanent magnet were employed.
The superposed incoming voice currents will then be able to vary this
magnetic field in exactly the same way as in the ordinary receiver.

An astonishing feature of this recent development of the so-called
direct-current receiver is that it did not come into use until after
about twenty years of common-battery practice. There is nothing new in
the principles involved, as all of them were already understood and
some of them were employed by Bell in his original telephone; in fact,
the idea had been advanced time and again, and thrown aside as not
being worth consideration. This is an illustration of a frequent
occurrence in the development of almost any rapidly growing art. Ideas
that are discarded as worthless in the early stages of the art are
finally picked up and made use of. The reason for this is that in some
cases the ideas come in advance of the art, or they are proposed
before the art is ready to use them. In other cases the idea as
originally proposed lacked some small but essential detail, or, as is
more often the case, the experimenter in the early days did not have
sufficient skill or knowledge to make it fit the requirements as he
saw them.

Monarch Receiver. The receiver of the Automatic Electric Company
just discussed employs but a single electromagnet by which the initial
magnetization of the cores and also the variable magnetization
necessary for speech reproduction is secured. The problem of the
direct-current receiver has been attacked in another way by Ernest E.
Yaxley, of th