that as far as the telephone was concerned it was immaterial whether it
was in circuit with a spiral or not, as in either case it accurately
reproduced the same sounds; therefore, much in the same way as lenses
assist the sight or tubes the hearing, so does the telephone make
manifest the lines of intermittent inductive energy. This was quite a
new phenomenon to me, and on further investigation of the subject I
found that it was not necessary to have even a telephone, for by simply
holding a piece of iron to my ear and placing it close to the center
of the spiral I could distinctly hear the same sounds as with the
telephone, although not so loud. The intensity of the sound was greatly
increased when the iron was placed in a magnetic field. Here is a small
disk of iron similar to those used in telephones, firmly secured in this
brass frame; this is a small permanent bar magnet, the marked end of
which is fixed very closely to, but not touching, the center of the iron
disk. Now, by applying the disk to my ear I can hear the same sounds
that were audible to all of you when the telephone in circuit with a
small spiral was placed in front of and close to the large spiral. To me
the sound is quite as loud as when you heard it; but now you are one and
all totally deaf to it. My original object in constructing two large
spirals was to ascertain whether the inductive lines of force given out
from one source would in any way interfere with those proceeding from
another source. By the aid of this simple iron disk and magnet it can be
ascertained that they do in no way interfere with each other; therefore,
the direction of the lines proceeding from each spiral can be distinctly
traced. For when the two spirals are placed parallel to each other at
a distance of 3 ft. apart, and connected to independent batteries and
transmitters, as shown in Plate 7, each transmitter having a sound
perfectly distinct from that of the other, when the circuits are
completed the separate sounds given out by the two transmitters can be
distinctly heard at the same time by the aid of a telephone; but, by