OPTOPHONE, an instrument invented by E. E. Fournier d'Albe in 1914 which enables the blind to read ordinary letter press such as printed books or newspapers. The invention thus places within reach of the blind the entire range of world litera ture, while previously their only means of reading—by raised letter systems—necessitated special books, both bulky and ex pensive.
The instrument depends for its action upon the chemical ele ment, selenium, the electrical conductivity of which varies greatly in accordance with the amount of light to which it is exposed. Such a light-sensitive selenium bridge is placed between two separate conducting lines of graphite resting on a porcelain tablet and the whole connected in series with an electric battery to a telephone receiver. A beam of light is rendered intermittent by the interposition of a revolving siren disc and is then concentrated into a small bright point on the letter to be read. This is reflected back onto the selenium bridge. As the selenium bridge is exposed to the forms of letters in the line traversed, its changes in con ductivity produce a succession of varying notes and chords in the telephone receiver, each letter having its characteristic sound.
That is its simple form. Actually in the regular instrument a row of five or six luminous points just filling up the size of the tallest letters to be read is substituted for a single point, and each point is given a different frequency by suitably perforating the disc. A blind reader does not analyze the resulting sounds, but soon comes to recognize the general sound of each letter and in time knows his alphabet of sounds. Later in his practice the succession of sounds which make up certain words becomes familiar. Con trolling apparatus to regulate the speed and position of the tracer is designed with a view to ease of manipulation by blind persons. After 192o developments in amplification enabled the sounds to be made audible to any number in a room if desired, though individual receivers were retained for silent reading. (See SELENIUM CELL.)