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Rh column of compressed air is controlled by a delicately adjusted grid-valve consisting of a metal comb rigidly connected to the stylus bar, so that as the needle moves the metal comb moves with it, following the lines of vibration fixed on the record and opening or closing the slots in the valve seat. The column of compressed air to which the valve gives access thus receives series of minute pulsations identical with those which originally produced the sounds recorded. In connexion with the sound-box is the apparatus for supplying compressed air, consisting of a sixth-horse power electric motor driving the compressor, an oil filter, a reservoir and a dust collector to keep the air absolutely free from foreign substances likely to interfere with the action of the valve.

The practical possibilities of the gramophone are being realized in many countries. Matrices of the records of well-known artists have been deposited at the British Museum and at the Grand Opéra in Paris. Austria established a public phonogram record office in 1903, in which are collected folk songs and records of all kinds for enriching the department of ethnography. The same idea is being carried out in Germany

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by private societies and by royal museums. In Hungary records of the various dialects have been secured. The possibilities of the gramophone as a teacher are far-reaching, not only in the domain of music but in learning languages, &c.

To understand how the phonograph records and reproduces musical tones, it is necessary to remember (1) that pitch or frequency depends on the number of vibrations executed by the vibrating body in a given period of time, or on the duration of each vibration; (2) that intensity or loudness depends on the amplitude of the movement of the vibrating body; and (3) that quality, timbre or clang, first, depends on the form of the individual vibrations, or rather on the power the ear possesses of appreciating a simple pendular vibration producing a pure tone, or of decomposing more or less completely a compound vibration into the simple pendular vibrations of which it is composed. If we apply this to the record of the phonograph, we find that, given a constant and sufficiently rapid velocity of the record, a note or tone of a certain pitch will be heard when the marker runs over a number of elevations and depressions corresponding to the frequency of that note. Thus if the note was produced by 200 vibrations per second, and suppose that it lasted in the music for $1⁄10$ of a second, 20 marks, each made in $1⁄200$ of a second, would be imprinted on the wax. Consequently, in reproduction, the marker would run over the 20 marks in $1⁄10$ of a second, and a tone of that frequency would be reproduced. The loudness would correspond to the depth of each individual mark on the cylinder or the width on the disk. The greater the depth of a series of successive marks produced by a loud tone, the greater, in reproduction, would be the amplitude of the excursions of the glass disk and the louder would be the tone reproduced. Lastly, the form of the marks corresponding to individual vibrations would determine the quality of the tone or note reproduced, by which we can distinguish the tone of one instrument from another, or the sensation produced by a tone of pure and simple quality, like that from a well-bowed tuning-fork or an open organ pipe, and that given by a trumpet or an orchestra, in which the sounds of many instruments are blended together. When the phonograph records the sound of an orchestra it does not record the tones of each instrument, but it imprints the form of impression corresponding to the very complex sound-wave formed by all the instruments combined. This particular form, infinitely varied, will reproduce backwards, as has been explained by acting on the glass plate, the particular form of sound-wave corresponding to the sound of the orchestra. Numerous instruments

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blend their tones to make one wave-form, and when one instrument predominates, if a human voice is singing to the accompaniment of the orchestra, another form of sound-wave, or rather a complex series of sound waves, is imprinted. When reproduced, the wave-forms again exist in the air as very complex variations of pressure; these act on the drum-head of the human ear, there is transmission to the brain, and there an analysis of the complex sensation takes place, and we distinguish the trombone from the oboe, or the human voice from the violin obbligato.

Many efforts have been made to obtain graphic tracings of wave-forms imprinted on the wax phonograph records. Thus J. G. M'Kendrick took (1) celloidin casts of the surface, and (2) micro photographs of a small portion of the cylinder (Journ. of Anat. and Phys., July 1895). He also devised a phonograph recorder by which the curves were much amplified (Trans. Roy. Soc. Edin., vol xxxviii.; Proc. Roy. Soc. Edin., 1896-1897, Opening Address; Sound and Speech Waves as revealed by the Phonograph, London, 1897; and Schafers, Physiol., vol. ii., "Vocal Sounds," p. 1229). As already mentioned, so long ago as 1878 Fleeming Jenkin and Ewing had examined the marks on the tinfoil phonograph. Professor Ludimar Hermann, of Konigsberg, took up the subject about 1890, using the wax-cylinder phonograph. He obtained photographs of the curves on the wax cylinder, a beam of light reflected from a small mirror attached to the vibrating disk of the phonograph being allowed to fall on a sensitive plate while the phonograph was slowly travelling. (For references to Hermann's important papers, see Schafer's Physiology, ii. 1222) Boeke, of Alkmaar, has devised an ingenious and accurate method of obtaining curves from the wax cylinder. He measured by means of a microscope the transverse diameter of the impressions on the surface of the cylinder, on different (generally equidistant) parts of the period, and he infers