The tutorial physics. Volume 1, A textbook of sound / by Edmund Catchpool.
- Catchpool, Edmund
- Date:
- [between 1890 and 1899]
Licence: Public Domain Mark
Credit: The tutorial physics. Volume 1, A textbook of sound / by Edmund Catchpool. Source: Wellcome Collection.
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![prong to this or any greater extent interchanges dark and light so rapidly that no hands are visible. [This effect is produced by an extremely feeble sound of exactly the frequency of the fork, hut not by very loud sounds of other frequencies. The method has been successfully used to investigate the question whether resultant tones exist outside the ear. (Art. 68).] 107. Phonograph.—Edison’s Phonograph is similar to the phonautograph in principle, but a cylinder covered with wax is substituted for the smoked one, and a very narrow chisel for the tracing point. The centre of the membrane is in this case made an antinode, and the point of the chisel therefore moves perpendicularly to the surface of the cylinder, not parallel to it, and so digs a trench of varying depth as the membrane vibrates. A section of this trench, parallel to its length and perpendicular to the surface of the cylinder, shows the form of the bottom, which depends on the quality of the sound, but is not the “ wave-form ” in any accurate sense of the term. It is, however, (like the trace of the phonauto- graph) a curve whose harmonic components are nearly the same as those of the waves. If the chisel is now replaced by a blunt point, and the cylinder, after being replaced in its original position, turned again in the same direction as at first the blunt point presses on the undulating bottom of the trench already cut by the chisel, and the membrane to which the point is connected repeats the movements by which the trench was originally cut. It thus produces waves in the air similar to those which, by their arrival, caused the original movements of the membrane, though they are reversed, the condensations of the original waves being represented by rarefactions in those afterwards produced by the membrane. Though in this and other respects there is con- siderable difference between the wave-forms of the original Bound and the sound reproduced by the membrane, the two have nearly the same harmonic components, and therefore seem to the ear so nearly of the same quality that, if the original sound was that of the speaking voice, the different vowels (which are only special qualities) are easily distinguished in the reproduction. It is worth noticing that it is the imperfection of the ear as a detector of differences in air waves that makes the phonograph and telephone possible. The waves they give](https://iiif.wellcomecollection.org/image/b28135441_0216.jp2/full/800%2C/0/default.jpg)
