There is a chemical element called selenium, which is peculiarly sensitive to light. When light shines upon selenium its electrical resistance is lowered, and hence it can be used as a light-operated valve to control the flow of electric current.
A MACHINE THAT READS PRINT
One of the most marvelous machines of the present day is one which will actually read ordinary printed type, uttering musical sounds that vary for each letter, so that a blind man after learning this new musical language can read any book. This machine, known as the optophone, is the invention of Prof. E. Fournier d’Albe, and was developed to a commercial success last year (1920). With it blind operators are able to read at the rate of twenty-five words per minute.
The operation of this wonderful machine can best be understood by reference to the accompanying diagrams, Figures 75 and 76.
Diagrammatic Arrangement of Optophone.
| FIG. 75.—END VIEW OF THE OPTOPHONE | FIG. 76.—SIDE VIEW OF THE OPTOPHONE |
There is an electric lamp in the machine before which there is a disk that is revolved by a small motor. In this disk there are five circular rows of slots and the light shining through these slots is cut up into five pulsating beams of light. These beams are brought to a focus in a vertical row upon the type page. From the paper they are reflected to a selenium cell or bridge. The selenium bridge forms part of the circuit of a telephone receiver and the diaphragm is thus made to vibrate at the same frequency as the light beams do. By varying the number of slots in each row in the disk the beams of light are given different periods of pulsation or vibration and they produce a sound chord or “scala” in the telephone receiver. The speed of the disk and the disposition of the slots is so chosen that the notes produced are G C′ D′ E′ G′ of the musical scale. Only white paper reflects the light beams; the black surface of the printed type absorbs them. Thus, as the row of beams is swept across a line of printed matter, the beams will be extinguished in various orders of succession, or simultaneously in accordance with the shape of the particular type-character they encounter.