Analysis of Articulate Sounds. 1 1 1 



this account the currents of the atmosphere in stormy seasons are 

 never regular, but blow and cease to blow by intervals ; as a part 

 of the moving stream is condensed by the projectile force; and 

 the succeeding part, being consequently rarefied, requires some time 

 to recover its density, and to follow the former part: this elasticity of 

 the air is likewise the cause of innumerable eddies in it; which are 

 much more frequent than in streams of water; as when it is impelled 

 against any oblique plane, it results with its elastic force added to its 

 progressive one. 



Hence when a vacuum is formed in the atmosphere, the sides of 

 the cavity forcibly rush together both by the general pressure of the 

 superincumbent air, and by the expansion of the elastic particles of 

 it; and thus produce a vibration of the atmosphere to a considerable 

 distance : this occurs, whether this vacuity of air be occasioned by 

 the discharge of cannon, in which the air is displaced by the sudden 

 evolution of heat, which as suddenly vanishes; or whether the vacuity 

 be left by a vibrating string, as it returns from each side of the arc, 

 in which it vibrates; or whether it be left under the lid of the valve 

 in the trumpet stop of an organ, or of a child's play trumpet, which 

 continues perpetually to open and close, when air is blown through 

 it; which is caused by the elasticity of the currents, as it occasions 

 the pausing gusts of wind mentioned above. 



Hence when a quick current of air is suddenly broken by any in- 

 tervening body, a vacuum is produced by the momentum of the pro- 

 ceeding current, between it and the intervening body; as beneath 

 the valve of the trumpet-stop above mentioned ; and a vibration is in 

 consequence produced; which with the great facility, which elastic 

 fluids possess of forming eddies, may explain the production of sounds 

 by blowing through a fissure upon a sharp edge in a common organ- 

 pipe or child's whistle; which has always appeared difficult to resolve; 

 for the less vibration an organ-pipe itself possesses, the more agreeable, 

 I am informed, is the tone; as the tone is produced by the vibration 

 of the air in the organ pipe, and not by that of the sides of it; though 

 the latter, when it exists, may alter the tone though not the note, 

 like the belly of a harpsichord, or violin. 



When a stream of air is blown on the edge of the aperture of. an 



