by the spark of a
Ruhmkorff's coil when the primary circuit is made and broken with
sufficient rapidity. When two breakers of different pitch are caused
simultaneously to open and close the primary circuit a double tone
proceeds from the spark.

A curious discovery, which may be of interest to you, has been made by
Professor Blake. He constructed a telephone in which a rod of soft iron,
about six feet in length, was used instead of a permanent magnet. A
friend sang a continuous musical tone into the mouthpiece of a
telephone, like that shown in Fig. 12, which was connected with the soft
iron instrument alluded to above. It was found that the loudness of the
sound produced in this telephone varied with the direction in which the
iron rod was held, and that the maximum effect was produced when the rod
was in the position of the dipping needle. This curious discovery of
Professor Blake has been verified by myself.

When a telephone is placed in circuit with a telegraph line the
telephone is found seemingly to emit sounds on its own account. The most
extraordinary noises are often produced, the causes of which are at
present very obscure. One class of sounds is produced by the inductive
influence of neighbouring wires and by leakage from them, the signals of
the Morse alphabet passing over neighbouring wires being audible in the
telephone, and another class can be traced to earth currents upon the
wire, a curious modification of this sound revealing the presence of
defective joints in the wire.

Professor Blake informs me that he has been able to use the railroad
track for conversational purposes in place of a telegraph wire, and he
further states that when only one telephone was connected with the track
the sounds of Morse operating were distinctly audible in the telephone,
although the nearest telegraph wires were at least fifty feet distant.

Professor Peirce has observed the most singular sounds produced from a
telephone in connection with a telegraph wire during the aurora
borealis, and I have just heard of a curious phenomenon lately observed
by Dr. Channing. In the city of Providence, Rhode Island, there is an
over-house wire about one mile in extent with a telephone at either end.
On one occasion the sound of music and singing was faintly audible in
one of the telephones. It seemed as if some one were practising vocal
music with a pianoforte accompaniment. The natural supposition was that
experiments were being