24 HISTORY OF ACOUSTICS. 



We begin our account of the Secondary Mechanical Sciences with 

 Acoustics, because the progress towards right theoretical views, was, in 

 fact, made much earlier in the science of Sound, than in those of Light 

 and of Heat ; and also, because a clear comprehension of the theory 

 to which we are led in this case, is the best preparation for the difficul- 

 ties (by no means inconsiderable) of the reasonings of theorists on thf 

 other subjects. 



CHAPTER I. 



PRELUDE TO THE SOLUTION OF PROBLEMS IN ACOUSTICS. 



IN some measure the true theory of sound was guessed by very eari) 

 speculators on the subject ; though undoubtedly conceived in a 

 very vague and wavering manner. That sound is caused by some 

 motion of the sounding body, and conveyed by some motion of the 

 air to the ear, is an opinion which we trace to the earliest times of 

 physical philosophy. We may take Aristotle as the best expounder 

 of this stage of opinion. In his Treatise On Sound and Hearing, he 

 says, " Sound takes place when bodies strike the air, not by the air 

 having a form impressed upon it (tf^fiari^o'iasvov), as some think, but 

 by its being moved in a corresponding manner ; (probably he means 

 in a manner corresponding to the impulse ;) the air being contracted, 

 and expanded, and overtaken, and again struck by the impulses of the 

 breath and of the strings. For when the breath falls upon and strikes 

 Jie air which is next it, the air is carried forwards with an impetus, 

 and that which is contiguous to the first is carried onwards; so that 

 the same voice spreads every way as far as the motion of the air takes 

 place." 



As is the case with all such specimens of ancient physics, different 

 persons would find in such a statement very different measures of 

 truth and distinctness. The admirers of antiquity might easily, by 

 pressing the language closely, and using the light of modern discovery, 

 detect in this passage an exact account of the production and propa- 

 ";ition of sound : while others might maintain that in Aristotle's own 



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iiiiul, there were only vague notions, and verbal generalizations. This 



