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A vibrating plate gives some sound always, even without 

 the tubes, for since there are at least eight waves, some one 

 will always be more favourably disposed for acting on the ear 

 than another, this difference will increase with the number 

 of waves ; and hence, the independent sound of a plate in- 

 creases in proportion as the vibrating portions into which it 

 divides, become more numerous. 



A string vibrating in free space, produces little or no 

 sound ; but if it be strung over, or in connexion with, an 

 elastic board or box, a great resonance is produced. This 

 arises from two sources ; first, the string when by itself is the 

 centre of two waves excessively close, and the action of which 

 is therefore interfering. But if the string ab, vibrate near a 

 ^ plane surface c, the wave — 1 , which passes 



towards it is reflected back, and meeting 

 the wave + 2, which follows, it neutralizes 

 ^ it partly, and enables the wave — 2, to 

 reach the ear without diminution. It is 



—2 



^ probable, however, that the great portion 

 of the sound arises from the board or plate 

 ^ itself vibrating in parts, or as a whole. If 



in parts, these parts are variously situated, as regards the 

 ear, and hence produce an effect upon it. Or if, as a whole, 

 the plate c is so broad, or bounded, if a box, that one wave 

 is lost by internal reflexion, and only the wave emanating from 

 the outer surface can arrive'at the ear. 



When a tuning fork is placed on a table, one wave is lost 

 by internal transmission and reflexions, whilst that directed 

 from the outer surface reaches to the ear. 



In the case of reed instruments, the reed produces two 

 waves, which, if it vibrated freely, should neutralize each 

 other on the ear ; but in practice whilst an open passage is al- 

 lowed to one by the mouth-piece, the other wave is lost 

 within the cavities of the lips and mouth. In mouth-piece 

 instruments, as bugles and trumpets, the cavity of the mouth 



^^ 



,+2 



