'I employ,' he says,
'the well known conducting effect of continuous metallic conductors as a
medium for sound, and increase the effect by electrically insulating
both the conductor and the parties who are communicating. It forms a
speaking telegraph without the necessity of any hollow tube.' In
connection with the telephone he used an electric alarm. It is by no
means evident from this description that Meucci had devised a
practicable speaking telephone; but he may have been the first to employ
electricity in connection with the transmission of speech. [Meucci is
dead.]
'This crowning marvel of the electric telegraph,' as Sir William Thomson
happily expressed it, was followed by another invention in some respects
even more remarkable. During the winter of 1878 Professor Bell was in
England, and while lecturing at the Royal Institution, London, he
conceived the idea of the photophone. It was known that crystalline
selenium is a substance peculiarly sensitive to light, for when a ray
strikes it an electric current passes far more easily through it than if
it were kept in the dark. It therefore occurred to Professor Bell that
if a telephone were connected in circuit with the current, and the ray
of light falling on the selenium was eclipsed by means of the vibrations
of sound, the current would undulate in keeping with the light, and the
telephone would emit a corresponding note.
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