ON MUSICAL INSTRUMENTS. 359 



pianoforte guitar, hammers are interposed between the fingers and the strings, 

 acting like those of tlie pianoforte. The mandoline and lute are species of 

 the guitar: and the arch lute was a very powerful instrument of the same kind, 

 formerly much ulsed in full pieces. 



In' the violin, and in other instruments resembling it, all the strings arc 

 capable of having their length altered at pleasure, by being pressed down on 

 the finger board. The sound is produced by the friction of the bow, rubbed 

 with resin: the string is carried forwards by its adhesion to the bow, and 

 when its resistance has overcome this adhesion, it begins to return in oppo- 

 sition to the friction ; for the friction of bodies in motion is generally less 

 than their adhesion when they are at rest with respect to each otlier, besides 

 that the contact of the string with the bow is usually in great measure in- 

 terrupted by subordinate vibrations, which may be distinguished, by the 

 assistance of a microscope, in the manner already described; but when the 

 string changes once more the direction of its motion, it adheres again to the 

 bow, and is accelerated by it as before. The original instrument appears to 

 have been the viola or tenor, its diminutive the violino, its intensitive, ex- 

 pressing a greater bulk, the violone or double bass, and the diminutive of 

 this,, the violoncello, or common bass. The viola di gamba had one or more 

 long strings separate from the finger board, serving as an occasional accom- 

 paniment. 



The vielle, or raonochorcl, commonly called the hurdy gurdy, has frets 

 which are raised by the action of the fingers on a row of keys; and instead 

 of a bow, the string is made to vibrate by the motion of a wooden wheel : 

 there is a second string serving as a drone, producing always the same sound ; 

 this is furnished with a bridge loosely fixed, which strikes continually against 

 the sounding board, and produces a peculiar nasal effect. The trumpet 

 marine, or trumpet Marigni, was a string of the same kind, which was 

 lightly touched at proper points, so as to produce harmonic notes only ; it was 

 impelled by a bow. The aeolian harp, when agitated by the wind, affords 

 a very smooth and delicate tone, frecpiently changing from one to another 

 of the harmonics of the string, accordingly as the force of the wind varies, 

 and as it acts more or less unequally on different parts of the string. (Plate 

 XXV. Fig. 356.) ' 



