[ 8? ] 



But many reafons concur to render us "fufpicious of the truth 

 of this reafoning : In the firft place, it is extremely improbable 

 that the water ftiould defcend in this regular catarad, leaving 

 the fluid in the ambient fpace at reft ; and it appears to be falfe 

 in fad, by obferving the motion of light particles fufpended in 

 the water, whofe motion does not appear to be confined within 

 the bounds of the catarad, or to be performed in that regular 

 curve which the reafoning requires. Secondly, Newton fuppofes 

 that the water which iffues with this velocity defcends from the 

 upper furface ; if this were fo, the fpouting fluid could not 

 attain its full velocity till a cylinder of it had 'been difcharged, 

 whofe bafe is equal to the area of the orifice, and height equal 

 to that of the fluid ; but this is not the cafe, for the loweft plate 

 or fmalleft quantity of the fluid will be difcharged with its full 

 velocity. Thirdly, fince the orifice is lefs than the upper furface 

 of the water, it would follow that the altitude I G would be 

 greater than HG; that is, the velocity of the fpouting fluid 

 would be greater than that which a heavy body would acquire 

 in falling through the height of the veflTel ; and that excefs would 

 be greater the larger the aperture ; fo that by encreafing the 

 aperture we might encreafe the velocity of the fpouting fluid 

 at pleafure. But this appears not by any means to be true in 

 fad ; for we can never produce, by any variation of the orifice, 

 a velocity greater than that which a heavy body would acquire 

 in falling through the height of. the fluid. 



Doctor Helsham's demonftration of this propofition is to 

 the following effed : If we fuppofe the column of water which 

 flands diredly over the orifice to be divided into an indefinite 

 number of plates of an equal, but exceedingly fmall thicknefs, 



we 



