SKCT. xvn.] A SPEAKING MACHINE. 169 



second new impulse. This reinforced sound will also be twice 

 reflected in time to conspire with the third new impulse ; and, 

 as the same process will be repeated on every new impulse, 

 each will combine with all its echoes to reinforce the sound 

 prodigiously. Professor Wheatstone, to whose ingenuity we 

 are indebted for so much new and valuable information on the 

 theory of sound, has given some very striking instances of 

 resonance. If one of the branches of a vibrating tuning-fork 

 be brought near the embouchure of a flute, the lateral aper- 

 tures of which are stopped so as to render it capable of pro- 

 ducing the same sound as the fork, the feeble and scarcely 

 audible sound of the fork will be augmented by the rich re- 

 sonance of the column of air within the flute, and the tone will 

 be full and clear. The sound will be found greatly to decrease 

 by closing or opening another aperture ; for the alteration in 

 the length of the column of air renders it no longer fit per- 

 fectly to reciprocate the sound of the fork. This experiment 

 may be made on a concert flute with a C tuning-fork. But 

 Professor Wheatstone observes, that in this case it is generally 

 necessary to finger the flute for B, because, when blown into 

 with the mouth, the under-lip partly covers the embouchure, 

 which renders the sound about a semitone flatter than it would 

 be were the embouchure entirely uncovered. He has also 

 shown, by the following experiment, that any one among 

 several simultaneous sounds may be rendered separately 

 audible. If two bottles be selected, and tuned by filling 

 them with such a quantity of water as will render them 

 unisonant with two tuning-forks which differ in pitch, on 

 bringing both of the vibrating tuning-forks to the mouth of 

 each bottle alternately, in each case that sound only will be 

 heard which is reciprocated by the unisonant bottle. 



Several attempts have been made to imitate the articulation 

 of the letters of the alphabet. About the year 1779, MM. 

 Kratzenstein of St. Petersburgh, and Kempelen of Vienna, 

 constructed instruments which articulated many letters, 

 words, and even sentences. Mr. Willis of Cambridge has 



