l8& Refonant Figures on Glafs. — Philofophlcal TranfaSltons. 



Thefe experiments have been lately repeated at Paris. In order to make them with fuccefs, 

 it is neceflary to take a fquare piece of glafs, three or four inches wide, not too thick, and 

 without either bubbles or knots. This plate is to be held firm between two very pointed 

 pieces of cork, and then powdered, with very fine fawduft or fand ; and when the bow of a 

 violin, well rorined, is drawn againfl the edge of the glafs, blunted or rounded by grinding, 

 a found will be produced, and, at the fame time, the powder will be feen to difpofe itfelf in 

 lines which afford different figures, according to the manner or place at which the glafs is 

 held, the bow is drawn, and the found produced. 



If, for example, the fquare be pinched by its centre, and the bow drawn along the middle 

 of one of its fides, the powder will difpofe itfelf in two lines, nearly diagonal to the fquare. 

 If the bow be drawn at the diftance of one-fourth of the fide from the angle, the two lines 

 will become the fides of an o6tagon, and the found will be the oftave of the preceding tone. 



By varying the pofitlon of the point at which the glafs is held, the figures alfo become 

 changed. 



If the plate of glafs be circular, and the bow be a little inclined, the fix radii of an hexagon 

 will be formed. 



In this manner, Mr. Chladni obtained i66 different figures, which he calls refonant figures. 

 Without prccifely explaining the caufe which produces thefe figures, their analogy with the 

 ftationary and vibrating parts of a mufical firing evidently fhews that the vibrating furface di- 

 vides itfelf into a number of portions which move feparately, but, no doubt, in an ifochronous 

 or commenfurate manner, when the tones are clear and mufical. The lines in which the 

 powder is coUedled, are a kind of gutters formed by the points which remain at refl, while the 

 other parts become alternately convex and concave, 



Thefe experiments, which fucceed equally with plates of metal, and even of wood, being 

 carefully made and clafTed fyftematically, promife to throw much light on the manner in which 

 furfaces vibrate, and may, perhaps, tend to the improvement of the theory of wind inftruments, 

 and other mufical apparatus, which is flill very imperfect, notwithflanding the labours of 

 Euler, in attempting to reduce them to computation. 



Decade Philof. No. 17. Art. VII.. 



Philofophtcal Tranfaflions of the Royal Society of London^ for the Tear 1799. Part the Firjl, 

 Quarto-, 156 Pages, with three Plates ; London, fold by Elmfly. 



This part contains, i. The Crobnian le£lure. Experiments and obfervations upon the flruc* 

 tiire of nerves. By Everard Home, efq; F.R.S. 2. The Bakerian leilure. Obfervations upon 

 an univerfal horizontal refraction of the air ; with remarks on the variations to which the 

 lower parts of the atmofphere are fometimes fubjedt. By the rev. S. Vince, A.M. F.R.S. and 

 plumian profefTor of aftronomy and experimental philofophy in the univerfity of Cambridge. 

 3, Abftrad of a regifter of the barometer, thermometer, and rain, at Lyndon, in Rutland, 1797. 



With 



