2012-08-13

Photophonic

The magazine The Engineer, on 21 January 1881, published an article describing Alexander Graham Bell's photophone. Here's a picture of it.

18810121bellphophoned1024
Looks so simple. As indeed it was. There's some text which goes with it but I've only cobbled together three columns of it. The above illustration is Figure 1 therein. See if you can spot the typo (hint - it's a mis-spelled adjective).

18810121photophonearticle
And here's the beginning of that text in machine-readablese (complete with aforementioned typo) so that search engines can pick it up.

BELL’S PHOTOPHONE.
During a recent visit to Paris, Professor Graham Bell favoured La Nature with an extended account of the investigations and discoveries which led to and resulted from his late remarkable invention, the photophone. He also supplied our scientific contemporary with details not previously made public, together with drawings of his apparatus an experiments, the engravings of which we here reproduce, with a translation of the account given by La Nature.

Our readers are already aware that the object of the photophone is the transmission of sounds both musical and vocal to a distance by the agency of a beam of light of varying intensity; and that the first successful attempts made Professor Bell and his co-labourer, Mr. Sumner Tainter, were based upon the known property of the element selenium, the electric resistance of which varies with the degree of illumination to which it is exposed. Hence, given a transmitting instrument, such as a fiexible mirror, by which the vibrations of a sound could throw into vibration a beam of light, a receiver, consisting of sensitive selenium, forming part of an electric circuit with a battery and a telephone, should suffice to translate the varying intensities of light into corresponding varying intensities of electric current, and finally into vibrations of the telephone disc audible once more as sound. This fundamental conception dates from 1878, when in lecturing before the Royal Institution, Professor Bell announced the possibility of hearing a shadow fall upon a piece of selenium included in a telephone circuit. The photophone, however, outgrew the particular electrical combination at suggested it; for not the least of the remarkable points in this research is the discovery that audible vibrations are set up in thin discs of almost every kind of material by merely throwing upon them an intermittent light. With the photophone as with the telephone, there are instruments of different degrees of perfection. The original telephone of Philip Reis could only transmit musical tones, because it worked by rapid abrupt interruptions of the electric current; while the articulating telephone of Graham Bell was able to transmit speech, since by its essential construction it was able to send undulating currents to the distant receiving station.

There now follows one of those glorious Victorian Etchings of a gentleman inventor:

18810121bellphophoneb1024

Which is figure 5 (as referred to in the text). Figure 6 brings in the second half of the double act:

18810121bellphophoneg1024

The staff writers at the magazine are by no means being over-familiar with their subjects - Graham and Sumner are of course the middle names, not the first names, of the two gentlemen in question.

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