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But water, as you know, is not necessary to the con- 

 duction of sound ; air is its most common vehicle. And 

 you know that when the air possesses the particular 

 density and elasticity corresponding to the temperature 

 of freezing water, the velocity of sound in it is 1,090 feet 

 a second. It is almost exactly one-fourth of the veloc- 

 ity in water ; the reason being that though the greater 

 weight of the water tends to diminish the velocity, the 

 enormous molecular elasticity of the liquid far more 

 than atones for the disadvantage due to weight. By 

 various contrivances we can compel the vibrations of 

 the air to declare themselves ; we know the length and 

 frequency of sonorous waves, and we have also obtained 

 great mastery over the various methods by which the 

 air is thrown into vibration. We know the phenomena 

 and laws of vibrating rods, of organ pipes, strings, 

 membranes, plates, and bells. We can abolish one 

 sound by another. We know the physical meaning of 

 music and noise, of harmony and discord. In short, as 

 regards sound we have a very clear notion of the exter- 

 nal physical processes which correspond to our sensa- 

 tions. 



In these phenomena of sound we travel a very little 

 way from downright sensible experience. Still the im- 

 agination is to some extent exercised. The bodily eye, 

 for example, cannot see the condensations and rarefac- 

 tions of the waves of sound. We construct them in 

 thought, and we believe as firmly in their existence as 

 in that of the air itself. But now our experience has to 

 be carried into a new region, where a new use is to be 

 made of it. 



Having mastered the cause and mechanism of 

 sound, we desire to know the cause and mechanism 



