76 



ON THE PHYSIOLOGICAL CAUSES OF 



sufficient accuracy to assign in some cases the form of 

 motion which they impart to the air. Thus Fig. 4 repre- 

 sents the forms successively assumed by a string struck, 

 as in the German Zither, by a pointed style, [the plectrum 



FIG. 4. 



of the ancient lyra, or the quill of the old harpsichord, 

 which may be easily imitated on a guitar]. A a represents 

 the form assumed by the string at the moment of percus- 

 sion. Then, at equal intervals of time, follow the forms 

 B, C, D, E, F, Gr ; and then in inverse order, F, E, D, C, 

 B, A, and so on in perpetual repetition. The form of 

 motion which such a string, by means of an attached sound- 

 ing board, imparts to the surrounding air, probably corre- 

 sponds to the broken line in Fig. 5, where h h indicates 

 the position of equilibrium, and the letters a b c d e f g 

 show the line of the wave which is produced by the action 



