e line to the receiving
end, and, in consequence, the possible length of line is limited to
a few miles, even under ideal conditions. With Edison's telephone the
battery current does not flow on the main line, but passes through
the primary circuit of an induction-coil, from the secondary of which
corresponding impulses of enormously higher potential are sent out on
the main line to the receiving end. In consequence, the line may be
hundreds of miles in length. No modern telephone system is in use to-day
that does not use these characteristic features: the varying resistance
and the induction-coil. The system inaugurated by Edison is shown by the
diagram (Fig. 3), in which the carbon transmitter, the induction-coil,
the line, and the distant receiver are respectively indicated.

In Fig. 4 an early form of the Edison carbon transmitter is represented
in sectional view.

The carbon disk is represented by the black portion, E, near the
diaphragm, A, placed between two platinum plates D and G, which are
connected in the battery circuit, as shown by the lines. A small
piece of rubber tubing, B, is attached to the centre of the metallic
diaphragm, and presses lightly against an ivory piece, F, which is
placed directly over one of the platinum plates. Whenever, therefore,
any motion is given to the diaphragm, it is immediately followed by a
corresponding pressure upon the carbon, and by a change of resistance in
the latter, as described above.

It is interesting to note the position which Edison occupies in
the telephone art from a legal standpoint. To this end the reader's
attention is called to a few extracts from a decision of Judge Brown
in two suits brought in the United States Circuit Court, District
of Massachusetts, by the American Bell Telephone Company against the
National Telephone Manufacturing Company, et al., and Century Telephone
Company, et al., reported in Federal Reporter, 109, page 976, et seq.
These suits were brought on the Berliner patent, which, it was claimed,
covered broadly the electrical transmission of speech by variations of
pressure between opposing electrodes in constant contact. The Berliner
patent was declared invalid, and in the course of a long and exhaustive
opinion, in which the state of art and the work of Bell, Edison,
Berliner, and others was fully discussed, the learned Judge made the
following remarks: "The carbon electrode was the invention of Edison....
Edison preceded Berliner in