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or as 7 to 5 nearly ; but the particles of the central filament ifTue 

 with the full velocity, due to the entire height of the water ; 

 therefore the velocity of the central particles will be to the mean 

 velocity, as 7 to the mean between 7 and 5, or as 7 to 6. This 

 is the diminution, as has been faid, which takes place in confe- 

 quence folely of the obliquity of the motions with which thtf 

 particles ifTue from the orifice : if the other caufes of retardation 

 be taken into the account, we may conclude, that the velocity 

 fhould be diminifhed perhaps in the ratio of 8 or even 9 to 6 ; 

 which accords very well with experiments. Thus Polenus makes 

 the ratio of the diameters of the contraifled vein and aperture, 

 which is the fame with that of the mean and greatefl velocity, 

 to be as 5I to 6^; Bernouilli 5 to 7 ; Chev. Du Buat 6 to 9. 

 When the orifice is infinitely little, the cylinder of iffuing water 

 becomes a fingle filament, which is therefore difcharged without 

 any obliquity, and there will be no diminution of velocity, 

 except fuch as arifes from fridion and the tenacity of the par- 

 ticles. If the aperture be encreafed fo as to become equal to the 

 bafe of the veflel, the column of water will then defcend like 

 a falling body, and therefore the velocity will be the fame as 

 before ; but it will not acquire this velocity until the uppermoft 

 plate of water has been difcharged. At the beginning of the 

 motion, the firft or loweft plate will flow out with a velocity 

 indefinitely little ; the next plate with a greater velocity ; and fo 

 on, until the upper plate fhall have defccnded to the orifice 

 which will then iflue with the greatefl velocity. But if the 

 Vol. VII. H vefTel 



