350 CALCULATIONS fob. 



In the foregoing elements (fee art. 4 and 5.) I have fappofed 

 the fpace which a heavy body defcribes by falling from reil in 

 one fccond of time to be 16 inftead of i6tt feet, and the 

 uniform velocity acquired by fuch fall =32 feet ; whereas every 

 author which I have read, (even on the fubjecl of hydraulics^ 

 makes it 32^ feet, without allowing for the friftion the water 

 is fubjefted to in its pafTage through the aperture or gateway, 

 or for the refiftence it meets with by its fudden impulfe againft 

 the air, immediately on its leaving the penftock. It evidently 

 follows that the uniform velocity muil be diminiflied on both thefe 

 accounts : hence we may fafely conclude, that a uniform velocity 

 of 32 feet in one fecond, will be found to coincide with an 

 experimental proof, nearer than that of 325 feet in the fame 

 time. 



Before the dimenfions of the fteam engine can be afcertained, 

 it is effentially neceflary to know what quantity of water it rouft 

 deliver into the penftock in a given time, in order that the 

 power or force by which the water-wheel is moved, may be 

 at leaft adequate to the purpofe intended. Several grift and 

 faw-mills have been examined with this view, and fuch meafure- 

 ments carefully taken as were thought neccffary for determining 

 the powers by which they are moved. Amongft thefe we have 

 felefted John Beydler's grill and faw-mills, and a faw-mill be- 

 longing to Chriftopher Keyger, both in the county of Berks and 

 ftate of Pennfylvania. 



Calculation of the power applied to Beydler's grist-mill, either for 

 one or tzuo pair of stones, each being ^\fcet in diameter, and 

 that of the luater-wheel 1 6 feet ; the top of which is nearly on 

 a level with the bottom of the penstock, and grinds from 50 t& 

 60 biifhels of wheat in 12 hours, with a Jingle pair of stones. 



The head or depth of Vi-ater from its furface to the bottom- 

 or the penftock for working one pair of ftones rr 22 inches. 



The gateway or aperture a is 30 inches wide by \i inch 

 deep zr 4^ inches :r: 0.3125 parts of a fquare loot. 



Mean heioht of the head, or D — • -- = Z> (art. 12.) rr 21' 



2 ^ 



inches nr 1.7; feet. 



By art. 7th we have %nq.^/h ■=. the number of ale gallons 



iiTuing through any aperture a in one fecond, z=. 8X0.31 2 ^X 



■ 6.3 2^ 



