236 



tion corresponding to the 5th on the string, but the 6th is 

 readily produced when the glass is vibrated by a violin 

 bow. 



These vibrations and the nodal divisions are made appa- 

 rent when the vibrated vessel is about half full of water, 

 the movement on the surface of which points out the 

 number of divisions in which the glass vibrates. 



But when plates of brass are employed, and the vibrations 

 are excited by a violin bow, harmonic vibrations may be 

 produced to a very considerable extent; and as was, I 

 believe, first observed by Chladni, the situation of the 

 nodal points, which in these instances become lines, are 

 very beautifully shown by strewing a little fine sand over 

 the plate, and wbich, by the violence of the vibration, is 

 thrown from the parts of the plate which are in strong 

 vibration, but remains on the lines formed by the portions 

 between the parts in vibration which remain quiescent. 



It might be supposed that the harmonies of plates would 

 follow in similar succession to those produced by strings ; 

 but this is not the case. However, the anomaly of these 

 tones may be resolved by the consideration that plates 

 vibrate differently, according to the manner in which they 

 are suspended; that is, a long plate suspended or fixed 

 at both ends, in a situation to vibrate, gives tones an octave 

 higher than a similar plate fixed at one end ; and a square 

 plate fixed at two of its sides, gives similar vibrations to 

 another square plate of four times the area, fixed on all 

 its sides ; as will be readily perceived on careful inspection 

 of the figures of sand on such plates. And it will be seen, 

 that on a reduction of all the vibrating portions of the 

 plate to that of figures bounded or fixed on all sides, the 

 vibrations will be those of ideal plates of diff'erent sizes; 

 and also that some parts of the plates between the figures 

 or vibrating portions are at rest ; thus accounting for the 



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