SUMMARY OF HYDRAULICS. 27 



its own motion, this plate would be urged by a force as much 

 greater than its own weight as the column is higher than itfelf; 

 and this, through a fpace fhorter in the fame proportion than 

 the height of the column. But where the forces are inverfely 

 as the fpaces defcribed, the final velocities are equal. (Young's 

 Syllabus, 35.) Therefore the velocity of the water flowing 

 out muft be equal to that of a heavy body falling from the 

 height of the head of water, which is found very nearly by 

 multiplying the fquare root of that height in feet by 8, for the 

 number of feet defcribed in a fecond. Thus a head of 1 foot 

 gives 8 ; a head of 9 feet, 24. 



The well-known circumftance of the contraction of the The contraction 

 ftream or vein of water running out of a fimple orifice in a thin ° e ream " 

 plate, reduces the area of its fection at the diflance of about 

 half its diameter from the orifice, from 1 to .660 or .666 ac- 

 cording to Boffut, to .631 according to Venturi, and to .64- or 

 ~y according to the author's own experiments : hence the 

 diameter is reduced to -J. 



The quantity of water difcharged is very nearly, but not Practical rule for 



quite, fufficient to fill this fedion with the velocity due, or cor- j^J&j**; 



refponding to the height: for finding more accurately the fquare root of 



quantity difcharged, the orifice mult be fuppofed to be dimi- t( ? e height by 5 



n 1 J , r-r 1. 1 1 r gives the velo- 



nitned to .619, or nearly -f-. Hence we may multiply the lquare city in 1 fecond, 



root of the height by 5 inftead of 8, for this mean velocity in a 



fimple orifice. 



If we apply the fiiorteft pipe that will caufe the ftream to Additional pipe 

 adhere every where to its fides, which will require its length to JjJ e ^? gt l tw,c * 

 be twice its diameter, the difcharge will be about ~| of the full the hole requires 

 quantity, and the velocity may be found by taking 6\ for a ^ l rnult] P I »er of 

 multiplier. 



The greateit diminution is produced by inferting a pipe fo Difadvantage of 

 as to project within the refervoir, probably becaufe of the greater an intenor P'P e J 

 interference of the motions of the particles approaching its 

 orifice in all directions : in this cafe the difcharge is reduced 

 nearly to a half. 



A conical tube, approaching to the figure of the contraction conical, &c. 

 of the ftream, procured a difcharge af .92 ; and when its edges PJ" oduced a dif - 

 were rounded off, of .98, calculating on its lead fection. 



Venturi * has aflerted that the difcharge of a cylindrical pipe Venturi's coni- 



cal tube j 

 * Venturi's treatife is given entire in our Journal, 4to, Vol. II. 

 and III. 



may 



