Transmission of Musical Sounds. 227 



In the guitar, lute, &c., the strings are also parallel to the 

 sounding-board, but the vibrations must, for the convenience 

 of performance, be made obliquely to it. If the sides of the 

 instrument be of inconsiderable depth, and the back be flat, the 

 difference of intensity between the perpendicular and oblique 

 vibrations will be very sensible. But if the sides be deep, very 

 little difference will be perceived, as the vibrations which are 

 tangential to the front sounding-board are perpendicular to 

 the sides, which thus enter readily into normal vibrations ; this 

 fact may be proved by placing the ear to the side of a guitar 

 while a string is made to sound with its plane of vibration suc- 

 cessively parallel and perpendicular to it. In some instru- 

 ments, as the lute, mandoline, &c. the back is polygonal or 

 curved ; by this construction a considerable portion of the re- 

 sonant surface enters into normal or nearly normal vibrations 

 when the strings are struck obliquely to the principal sounding- 

 board. 



These laws are not so immediately applicable to the violin, 

 and other instruments of the same class ; an extensive series of 

 experiments will yet be necessary to enable us to account for 

 the peculiarities of their forms, their various curvatures, and 

 the functions of that irregular conductor, resting on the sound- 

 ing-board at two points only, which in these instruments is 

 called the bridge. The investigations of Savart still leave 

 much to be desired on this head. 



In no instrument are the strings perpendicular to the sound- 

 ing-board ; for in such case, however a string were made to 

 vibrate, its communicated vibrations would be tangential. But 

 they are sometimes placed obliquely, as in the harp, and then the 

 same changes of intensity may be observed as when the strings 

 are parallel to the board ; for if the plane of their vibrations 

 coincide with that of the inclination of the board, the commu- 

 nicated vibrations of the board will be oblique to its surface, 

 and the intensity will be at its maximum ; but if they be per- 

 pendicular to this plane, the communicated vibrations must 

 be tangential to this surface, and consequently the intensity 

 will be at its minimum. 



Besides the proper adaptation of sounding-boards, there are 

 other circumstances on which the tones of a stringed instrument 



