Radiophony

As radiophony (lat.-Greek.) Is defined as the sound excitation by radiation or the generation of a tone by the action of an interrupted at regular intervals ( "intermittent") light beam on a thin plate of any solid body wherein the vibration frequency of the sound is equal to the number of interruptions of the light beam in one second.

Procedure

The interruptions ( intermittences ) of the light beam are z. B. produced with the help of a rotating glass plate, which is pasted with dark paper, in which the openings for the passage of the rays are cut on the edge.

The sounding plate is either held directly to the ear or placed in the wider opening of a small hearing tube, from the narrower end of which a rubber tube leads to the ear. The strength of the sound heard is mainly determined by the nature of the surface of the plate and is significantly increased if this surface is covered with soot , platinum black , asphalt, etc., which strongly absorb the rays.

From these facts it can be seen that there is a surface effect in which the plate itself does not participate, and in fact substances of a loose structure, such as cotton , cork , sponge, etc., emit intermittent light irradiated in a horn closed with a glass plate , louder tones than other fabrics, especially if they were darkly colored or, even better, blackened with soot; Wire cloth blackened with soot or lamp soot alone also proves to be very effective.

A very simple and effective radiophone is obtained by inserting a flexible mica plate covered with soot into a test tube and allowing the rays to fall onto the layer of soot so that they first pass the transparent wall of the glass opposite. The open end of the tube is connected to a hearing tube with a rubber tube ; In this way, when using Drummond's light , the radiophonic tones can be heard up to a distance of 1 to 2 m from the mouth of the ear trumpet.

If one wants to use this device not only to reproduce musical tones and chords, as the perforated disc gives them, but to reproduce the articulated sounds of human speech, this is achieved by the same means that Alexander Graham Bell used for his selenium photophonically , by turning on the light beam a thin, flexible mirror, which is shaken by the words spoken against its back, which are communicated to the reflected light beam. If the light beam is concentrated on the soot layer of the radiophone by means of a lens, the spoken words can be clearly heard from this.

This simple device, like Bell's photophone, makes the light beam the carrier of the human voice without the aid of a galvanic battery or a telephone .

functionality

Ernest Mercadier has shown that the Radiophonic sounds most by red and infra-red (ie infrared are produced) rays, that is, by those rays whose warming effect is the largest, while the effect on the selenium that the Bell's photophone underlies , preferably attributable to the shining rays. Mercadier has therefore proposed the term thermophony instead of radiophony .

The radiophonic tones arise from the fact that the loose bodies in the spaces between the particles, e.g. B. the soot , contained air is alternately heated and expanded, then cools down again and contracts and so gets into audible vibrations.

Gases and vapors, which are enclosed in small glass flasks, from the mouth of which a rubber tube leads to the ear, are, as Tyndall has shown, made to sound by intermittent rays that are dropped on the neck of the flask, and all the more so , the greater its absorption capacity for the incident rays.

If the intermittent light is spread out to a spectrum, a body will sound most powerfully in that part of the spectrum for which it has the greatest absorption capacity . The points of strongest absorption, at which dark absorption stripes would show up to the eye, can therefore also be perceived by hearing.

For this purpose, Bell set up an apparatus called a spectrophone , which is nothing more than a spectroscope whose eyepiece has been replaced by an ear tube.

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This article is based on a text in the public domain from Meyers Konversations-Lexikon , 4th edition from 1888 to 1890.

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Radiophony . In: Meyers Konversations-Lexikon . 4th edition. Volume 13, Verlag des Bibliographisches Institut, Leipzig / Vienna 1885–1892, p. 542.