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What is here faid of the velocity of t!ie effluent water is true 

 only of the middle filament of particles which iflue through the 

 centre of the aperture, and which fuffer no other retardation 

 than what arifes from the refiftance of the air, and their mutual 

 adhefion and attrition againfl each other. But thofe which iffue 

 near the edges of the aperture undergo a greater attrition, and 

 therefore fufFer a greater retardation. Hence it follows, that the 

 mean velocity of the whole column of effluent water will be 

 confiderably lefs than according to theory. 



Sir Ifaac Newton, who examined every fubjed that came 

 before him with peculiar accuracy, firft difcovered a contra<Slion 

 in the vein of effluent water ; and he found, that at the diftancc 

 of about a diameter of the orifice, the fedlion of the vein con- 

 traded nearly in the fubduplicate ratio of 2 to i. Hence he 

 concluded that the velocity of the water, after its exit from the 

 aperture, was encreafed in this proportion, the fame quantity 

 paffing in the fame time through a narrower fpacc. Now, from 

 the quantity of water difcharged in a given time through that 

 narrow fedion, he found that its velocity there was that which a 

 heavy body would acquire in falling through the height of the 

 water above the orifice ; and fince the velocity there was greater 

 than immediately in the orifice in the fubduplicate ratio of 2 to i, 

 he concluded that the velocity of the effluent water in the orifice 

 was equal to that which a heavy body would acquire in falling 

 through half the altitude. But all this is true only of the mean 

 velocity ; for there is no caufe which can adually accelerate the 

 water after its exit from the orifice, whatever caufes may con- 

 tribute to its retardation. The manner in which the mean velo- 

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