Eptperlmeitts and hquirles refpeFllng Sound and Light. 125 



the bow was ftrung with the fecond ftring of a violin : and, in the preparatory application 

 of refin, the longitudinal found of Chladni was fometimes heard ; but it was obferved to 

 difFer at leaft a note in different parts of the ftring. 



XIV. Of the Vibrations of Rods and Plates. 

 Some experiments were made, with the affiftance of a moft excellent praftical mufician, 

 on the various notes produced by a glafs tube, an iron rod, and a wooden ruler ; and, in 

 a cafe where the tube was as much at liberty as poflible, all the harmonics correfponding to 

 the numbers from i to 13, were diftindly obferved; feveral of them at the fame time, 

 and others by means of different blows. This refult feems to differ from the calculations 

 of Euler and Count Riccati, confirmed as they are by the repeated experiments of Profeffor 

 Chladni ; it is not therefore brought forward as fufficiently controverting thofe calculations, 

 but as fliowing the neceffity of a revifion of the experiments. Scarcely any note could 

 ever be heard when a rod was loofely held at its extremity ; nor when it was held in the 

 middle, and ftruck one-feventh of the length from one end. The very ingenious method 

 of Profeffor Chladni, of obferving the vibrations of plates by ftrewing fine fand over them, 

 and difcoverlng the quiefcent lines by the figures into which it is thrown, has hitherro 

 been little known in this country : his treatife on the phaenomena is fo complete, that 

 no other experiments of the kind were thought neceffary. Glafs veffels of various de- 

 fcriptions, whether made to found by percuffion or friftion, were found to be almofl: 

 intirely free from harmonic notes } and this obfervation coincides with the experiments 

 of Chladni. 



XV. Of the Human Voice. 



The human voice, which was the obje£t originally propofed to be illuftrated by thefe 

 refearches, is of fo complicated a naiure, and fo imperfe£lly underftood, that it can be on 

 this occafion but fuperficially confidered. No perfon, unlefs we except M. Ferrein, has 

 publifhed any thing very important on the fubje£t of the formation of the voice, before 

 or fince Dodart ; his reafoning has fully fliown the analogy between the voice and the 

 iHiix humaine and regal organ-pipes : but his comparifon with the whiftle is unfortunate ; 

 nor is he more happy in his account of the falfetto. A kind of experimental analyfis of 

 the voice may be thus exhibited. By drawing in the breath, and at the fame time pro- 

 perly contra£ting the larynx, a flow vibration of the ligaments of the glottis may be 

 produced, making a diftinft clicking found ; upon increafing the tenfion, and the velocity 

 of the breath, this clicking is loft, and the found becomes continuous, but of an extremely 

 grave pitch ; it may, by a good ear, be diftinguiflied two oftaves below the loweft A of a 

 common bafs voice, confifting in that cafe of about 26 vibrations in a fecond. The fame 

 found may be raifed nearly to the pitch of the common voice ; but it is never fmooth and 

 clear, except perhaps in fome of thofe perfons called ventriloqulfts. When the pitch is 

 raifed ftill higher, the upper orifice of the larynx, formed by the fummits of the arytsenoid 



cartilages 



