respecting Sound and Light. 141 



they are by the repeated experiments of Professor Chladni ; it 

 is not therefore brought forward as sufficiently controverting 

 those calculations, but as showing the necessity of a revision of 

 the experiments. Scarcely any note could ever be heard when 

 a rod was loosely held at its extremity ; nor when it was held 

 in the middle, and struck one-seventh of the length from one 

 end. The very ingenious method of Professor Chladni, of 

 observing the vibrations of plates by strewing fine sand over 

 them, and discovering the quiescent lines by the figures into 

 which it is thrown, has hitherto been little known in this 

 country : his treatise on the phenomena is so complete, that no 

 other experiments of the kind were thought necessary. Glass 

 vessels of various descriptions, whether made to sound by per- 

 cussion or friction, were found to be almost intirely free from 

 harmonic notes ; and this observation coincides with the expe- 

 riments of Chladni. 



XV. Of the human Voice. 



The human voice, which was the object originally proposed to 

 be illustrated by these researches, is of so complicated a nature, 

 and so imperfectly understood, that it can be on this occasion but 

 superficially considered. No person, unless we except M. Fer- 

 rein, has published any thing very important on the subject of 

 the formation of the voice, before or since Dodart; his reason- 

 ing has fully shown the analogy between the voice and the voir 

 humaine and regal organ-pipes : but his comparison with the 

 whistle is unfortunate; nor is he more happy in his account of the 

 falsetto. A kind of experimental analysis of the voice may be 

 thus exhibited. By drawing in the breath, and at the same time 

 properly contracting the larynx, a slow vibration of the ligaments 

 of the glottis may be produced, making a distinct clicking sound : 



