n8 Dr. Young's Experiments and Inquiries 



problems relating to the subject ; yet some of his assumptions 

 are not only gratuitous, but contrary to matter of fact. 



VI. Of the Divergence of Sound. 



It has been generally asserted, chiefly on the authority of 

 Newton, that if any sound be admitted through an aperture 

 into a chamber, it will diverge from that aperture equally in all 

 directions. The chief arguments in favour of this opinion are 

 deduced from considering the phenomena of the pressure of 

 fluids, and the motion of waves excited in a pool of water. But 

 the inference seems to be too hastily drawn : there is a very 

 material difference between impulse and pressure ; and, in the 

 case of waves' of water, the moving force at each point is the 

 power of gravity, which, acting primarily in a perpendicular 

 direction, is only secondarily converted into a horizontal force, 

 in the direction of the progress of the waves, being at each step 

 disposed to spread equally in every direction : but the impulse 

 transmitted by an elastic fluid, acts primarily in the direction of 

 its progress. It is well known, that if a person calls to another 

 with a speaking trumpet, he points it towards the place where 

 his hearer stands : and I am assured by a very respectable 

 Member of the Royal Society, that the report of a cannon 

 appears many times louder to a person towards whom it is 

 fired, than to one placed in a contrary direction. It must have 

 occurred to every one's observation, that a sound such as that 

 of a mill, or a fall of water, has appeared much louder after 

 turning a corner, when the house or other obstacle no longer 

 intervened; and it has been already remarked by Euler, on this 

 head, that we are not acquainted with any substance perfectly 



