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LECTURE XXXIV. 



ON MUSICAL INSTRUMENTS. 



The application of the theory of harmonics to practice depends on the 

 construction of musical instruments of different kinds: of these we shall 

 only be able to take a cursory view, and we shall afterwards attend to the 

 historical order of the most remarkable steps, by which both the theory and 

 practice of music have been advanced to a high degree of refinement. 



Musical instruments may be most conveniently arranged, accordingly 

 as they are principally calculated for exciting sound by the vibrations 

 of chords, of membranes, of elastic plates, or of the air; or by the 

 joint effects of the air and a solid body vibrating together. The es- 

 sential varieties of stringed instruments are found in the harp, the 

 harpsichord, the pianoforte, the clavichord, the guitar, the violin, the 

 vielle or monochord, and the aeolian harp. In all these, the immediate force 

 of the sound of the strings is increased by means of a sounding board, which 

 appears to be agitated by their motion, and to act more powerfully on the 

 air than the strings could do alone. 



In the harp, the sound is produced by inflecting the string with the 

 finger, and suffering it to return to its place. The lyre of the ancients 

 differed from the harp only in its form and compass, except that the per- 

 former sometimes used a plectrum, which was a small instrument, made of 

 ivory, or some other substance, for striking the strings. Each note in the 

 harp has a separate string; and in the Welch harp there are two strings to 

 each note of the principal scale, with an intermediate row for the ficm'tones; 

 but in the pedal harp, the half notes are formed by pressing pins against the 

 strings, so as to shorten their effective length. Instead of this method, an 

 attempt has lately been made to pxoduce the semitones by changing the 



