on of an intermittent
current from the fork _b_. Resonators, 1, 2, 3, etc., are arranged so as
to reinforce the sounds in a greater or less degree, according as the
exterior orifices are enlarged or contracted.

[Illustration: Fig. 3]

Thus it will be seen that upon Helmholtz's plan the tuning forks
themselves produce tones of uniform intensity, the loudness being varied
by an external reinforcement; but it struck me that the same results
would be obtained, and in a much more perfect manner, by causing the
tuning forks themselves to vibrate with different degrees of amplitude.
I therefore devised the apparatus shown in Fig. 3, which was my first
form of articulating telephone. In this figure a harp of steel rods is
employed, attached to the poles of a permanent magnet, N. S. When any
one of the rods is thrown into vibration an undulatory current is
produced in the coils of the electro-magnet E, and the electro-magnet E'
attracts the rods of the harp H' with a varying force, throwing into
vibration that rod which is in unison with that vibrating at the other
end of the circuit. Not only so, but the amplitude of vibration in the
one will determine the amplitude of vibration in the other, for the
intensity of the induced current is determined by the amplitude of the
inducing vibration, and the amplitude of the vibration at the receiving
end depends upon the intensity of the attractive impulses. When we sing
into a piano, certain of the strings of the instrument are set in
vibration sympathetically by the action of the voice with different
degrees of amplitude, and a sound, which is an approximation to the
vowel uttered, is produced from the piano. Theory shows that, had the
piano a very much larger number of strings to the octave, the vowel
sounds would be perfectly reproduced. My idea of the action of the
apparatus, shown in Fig. 3, was this: Utter a sound in the neighbourhood
of the harp H, and certain of the rods would be thrown into vibration
with different amplitudes. At the other end of the circuit the
corresponding rods of the harp H would vibrate with their proper
relations of force, and the _timbre_ [characteristic quality] of the
sound would be reproduced. The expense of constructing such an apparatus
as that shown in figure 3 deterred me from making the attempt, and I
sought to simplify the apparatus before venturing to have it made.

[Illustration: Fig. 4]

[Illustration: Fig. 5]

[Illustration: Fig. 6]