Van Nostrand's eclectic engineering magazine . Voodhead Tunnel, millstone, Burn . Vallev Hill,ft. ft. 40 to 700400 to 2600110 to 700 10 to200 to 30 to70 to 600500 600350 150 to 500150 to 500800 to 1500 1000750 to 1600 V 3 a a to ^ &l .« (U ti 2 < CJ •£5 c5 .i2 a P S G. Q EH « W Pq. eft. c. ft. miles. per min. per min. 3086 40,000 3900 3,000 5,000 1,200 570 0 8,880 3 53 1,800 9 93 2,209 4 59 1 04 481 5 2,520 5 23 1,800 3 37 69 5 2,500 8 19 500139130 15.
Van Nostrand's eclectic engineering magazine . Voodhead Tunnel, millstone, Burn . Vallev Hill,ft. ft. 40 to 700400 to 2600110 to 700 10 to200 to 30 to70 to 600500 600350 150 to 500150 to 500800 to 1500 1000750 to 1600 V 3 a a to ^ &l .« (U ti 2 < CJ •£5 c5 .i2 a P S G. Q EH « W Pq. eft. c. ft. miles. per min. per min. 3086 40,000 3900 3,000 5,000 1,200 570 0 8,880 3 53 1,800 9 93 2,209 4 59 1 04 481 5 2,520 5 23 1,800 3 37 69 5 2,500 8 19 500139130 21 6 ts. t: •2514 23 45 0 46 unit adopted in calculations is a foot; andthe unit of water being taken at a cubicfoot, weighing lbs., the resulting pro-duct from the multiplication of the threequantities will give the pressure in poundson the surface immersed. Let it be sup-posed, for simplicity, that water to thedepth of 10 ft. has to be sustained by avertical rectangular wall, as in Fig. 5. It. is usual to take but 1 it length of thewall for the calculation, though it will notafiect the result whether 1 ft. or 100 ft. We then have be the length assumed. the surface under pressure = 10 sq. ft, thedepth of the centre of gravity = 5 ft., andthe weight of a cubic foot = lbs., theproduct of which quantities gives us 3,125lbs. pressure on 1 ft. length of the wall. Butthis pressure is not the whole of the forcethat the wall has to resist; the leveragethat it exerts must also be taken intoaccount. In the example under consider-ation—viz. that of a vertical plane with oneof its sides coinciding with the surface ofthe water, as in Fig. 5—the whole of thepressure is so distributed as to be equal toa single force acting at a point one-third ofthe depth from the bottom. Thus, thetotal force to be resisted by the wall is3125 X = 10,406, whichis the momenttending to overturn the wall. It is evident that a certain weight of thewall mu
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