312 LECTURE XXXIV. 



strings, acting like those of the pianoforte. The mandolinfess^d lute 

 species of the guitar : and the arch lute was a very powerful instrument of 

 the same kind, formerly much used in full pieces. 



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

 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 opposition to the friction ; for the friction of bodies in motion is gene- 

 rally less than their adhesion when they are at rest with respect to ach 

 other, besides that the contact of the string with the bow is usually in great 

 measure interrupted 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 instru- 

 ment appears to have been the viola or tenor, its diminutive the violino, its 

 intensitive, expressing 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 accompaniment. 



The vielle, or monochord, 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 continu- 

 ally 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, frequently 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.) 



The human voice depends principally on the vibrations of the mem- 

 branes of the glottis, excited by a current of air, which they alternately 

 intercept and suffer to pass ; the sounds being also modified in their sub- 

 sequent progress through the mouth. Perhaps the interception of the air 

 by these membranes is only partial ; or it may be more or less completely 

 intercepted in sounds of different kinds : the operation of the organs con- 

 cerned is not indeed perfectly understood, but from a knowledge of their 

 structure, we may judge in some measure of the manner in which they are 

 employed. 



The trachea, or windpipe, conveys the air from the chest, which serves 

 for bellows : hence, it enters the larynx, which is principally composed of 

 five elastic cartilages. The lowest of these is the cricoid cartilage, a strong 

 ring, which forms the basis of the rest : to this are fixed, before, the thy< 

 reoid cartilage, and behind, the two arytaenoid cartilages, composing 

 together the cavity of the glottis, over which the epiglottis inclines back- 



