As the height of the notes of the musical scale depends on the number of vibrations effected by a vibrating substance in a given time, speaking will be reproduced in a tone of which the pitch will depend on the velocity of rotation given to the cylinder on which the tinfoil is wound. If the velocity is the same as that which was used in registration, the tone of the words reproduced is the same as that in which they were uttered. If the velocity is greater, the tone is higher; if less, the tone is lower; but the accent of the speaker may always be recognised. Owing to this peculiarity the reproduction of songs is nearly always defective in instruments turned by the hand; they sing out of tune. This is not the case when the instrument is moved by a well-regulated system of clockwork, and in this way a satisfactory reproduction of a duet has been obtained. The words registered on tinfoil can be often reproduced; but the sounds become fainter and more indistinct at each repetition, since the tracings in relief are gradually effaced. The reproduction on copper is more successful, but if intended to be permanent the sheets must be stereotyped, and in this case the instrument must be differently arranged. An attempt has been made to obtain speech from the phonograph by taking the words registered inversely to their true direction. In this way the sounds obtained were necessarily quite unlike the words uttered; yet Messrs. Fleeming Jenkin and Ewing have observed that not only are the vowels unchanged by this inverse action, but consonants, syllables, and even whole words may be reproduced with the accent they would have if spoken backwards. The sounds produced by the phonograph, although fainter than those of the voice which produced the registered tracing, are strong enough to react on the ordinary string telephone, and even on a Bell telephone; and as in this case the sounds do not go beyond the instrument, and can only be heard by the person who is using it, it is easy to ascertain that the sound has not been produced by trickery.