the make and break of the contact between the diaphragm _1_ and the
point _2_ interrupt the line circuit. His receiver took several forms,
all electromagnetic. His success was limited to the transmission of
musical sounds, and it is not believed that articulate speech ever was
transmitted by such an arrangement.

It must be remembered that the art of telegraphy, particularly in
America, was well established long before the invention of the
telephone, and that an arrangement of keys, relays, and a battery, as
shown in Fig. 5, was well known to a great many persons. Attaching the
armatures of the relays of such a line to diaphragms, as in Fig. 6, at
any time after 1838, would have produced the telephone. "The hardihood
of invention" to conceive such a change was the quality required.

[Illustration: Fig. 5. Typical Telegraph Line]

Limitations of Magneto Transmitter. For reasons not finally
established, the ability of the magneto telephone to produce large
currents from large sounds is not equal to its ability to produce
large sounds from large currents. As a receiving device, it is
unexcelled, and but slight improvement has been made since its first
invention. It is inadequate as a transmitter, and as early as 1876,
Professor Bell exhibited other means than electromagnetic action for
producing the varying currents as a consequence of diaphragm motion.
Much other inventive effort was addressed to this problem, the aim of
all being to send out more robust voice currents.

[Illustration: Fig. 6. Telegraph Equipment Converted into Telephone
Equipment]