Manner in which Sound is produced. 199 



The analogy between sound and light has been noted as 

 remarkable, though it has not been carried out far enough ; 

 and as light and heat have been admitted to be distinct en- 

 tities, and as they have distinct organs of sense (the eye and 

 the skin), appointed to them ; and as taste and smell are 

 also made known by motion, and contact with distinct or- 

 gans ; and as there is a distinct organ appropriated to sound, 

 there is no reason why it should not be regarded also as a 

 distinct entity, though, hitherto, our observation has not 

 been extended far enough to shew that it is such. If we 

 once begin to discover anything hitherto unobserved respect- 

 ing sound, its philosophy may again advance, and become as 

 interesting, perhaps, as that of electricity, heat, or light. 



That the mere action of one solid body on another solid 

 body is not essential to the production of sound, is proved 

 by the mechanical action or motion of a bell in vacuo pro- 

 ducing none. The same fact proves the necessity for the 

 presence of air ; and this renders the affirmation safe, that, 

 while it is undeniable the action of various substances in 

 certain circumstances on each other, produces the condition 

 necessary for the evolvement of sound, neither the action, 

 nor the condition it brings about (motion), can be considered 

 as the thing evolved under that condition. 



The ordinary inference from the experiment of the bell 

 in vacuo, is, that air is necessary for the conduction of sound. 

 My inference seems equally just, that it is as necessary for 

 the production of sound. The first inference implies, that 

 sound is actually produced by the bell in vacuo, but is not 

 heard on account of a conductor being absent. If air is re- 

 garded as a conductor merely, the experiment proves some- 

 what more, viz., that none of the materials of which the ap- 

 paratus for performing the experiment consists, can be con- 

 sidered as generators of sound. If they were, sound should 

 be heard, if produced by the bell. As no sound is heard, the 

 inference is irresistible, that air is necessary to its produc- 

 tion. This, then, is one fact decidedly established by the ex- 

 periment. 



The question that now occurs is, How comes air to be ne- 

 cessary to the production of sound ? And this involves an- 



