WATER. 



Few machines, with pumps worked by a water-wheel, 

 will raife more water to a given height in any time, than 

 amounts to one-third the mechanical effeft of the quantity of 

 water employed to work it ; that is, confidering the dif- 

 ferences of the heights to which the water is raifed, and the 

 height of the fall, and reducing them both to an equahty, 

 the quantity of water raifed will never exceed half of the 



quantity which falls. The other half is loft in friftion an J. 

 leakage, and in overcoming the inertia of the parts of the 

 machine. 



Prejfure engines are thofe machines which give motion to 

 the piilon of a pump, by the force of a column of 

 water afting in a cylinder or barrel, fimilar to that of 

 the pump. ( See the article PRES.suRE-^n^inf. ) It was 

 omitted in that article, that M. Belidor invented a ma- 

 chine, which may be confidered as the firft which was 

 perfeft, and was indeed the model for that made by 

 Mr. Smeaton. See Architefture Hydraulique, vol. ii. 

 p. 240. 



M. Baillet made obfervations upon feveral machines of 

 this kind in the mines of Hungary, from which it appears 

 that the mechanical effeil produced, is only four-tenths of 

 the mechanical efFedt of the iirft power. 



The French metre is equal to 3.281 Englifh feet, and the 

 cubic metre is 35.3198 cubic feet Enghlh. 



Poiuer of the largejl Steam-Engines to raife Water. — The 

 moft powerful machine in exiftence is the ileam-engine, on 

 Mr. Watt's principle, called Stoddart's engine, at the 

 United Mine in Cornwall. Three other engines of equal 

 dimenfions are employed to drain the mine, but only this 

 one is loaded fo as to exert its utmolt force. The fteam 

 cyhnder is 63 inches diameter, and aAs double ; that is, it 

 operates to raife water equally in the afcent or defcent of 

 the pifton. The weight of water in the pumps is 82,000 

 pounds, and with this load it makes 65 double flrokes per 

 minute of 7^ feet each ; or, it gives to the load loof feet 

 motion per minute. 



Multiply 82,000 pounds by looy feet, and it gives 

 8,261,500 pounds /icr minute lifted one foot high: divide 

 this by 33,000 pounds, which is called the horfe-power, and 

 it gives 2505 horfe-power for the afting force of the engine. 

 Again, divide 8,261,500 pounds by 62^ pounds, the weight 

 of a cubic foot of water, and we tind this engine is capable 

 of raifing 1 32, 1 84 cubic feet of water per minute to a height 

 of one foot. This is not one of the beft engines with re- 

 fpeft to fuel, and it burns 3 1 \ pounds of coal to raife this 

 quantity. 



The whole power employed to drain the United Mine is 

 as follows : 



Horfe-Power. 

 Stoddart's engine, 63 inch cylinder, double afting 25OJ 

 William's engme, 65 inch cyhnder, do. 200 



Sim's engine, 63 inch cylinder, do. 185 



Poldorey's engine, 63 inch cylinder, do. 196 



Total - 83 1 i 



Here we liave a fingle machine of nearly double the 

 power of the famous machine at Marly, which is in faft 

 compofed of fourteen machines, working in concert for a 

 common objeift ; and fo do the four engines in the mine, 

 which amount to 83 I 3 horfe-power, without reckoning the 

 engines employed to draw up the ore. 



The engines at feveral other mines in Cornwall are of 

 immenfc power. We will ftate two. 



The mine called Wheal Alfred has four engines : a 

 63 inch double engine, which is lightly loaded, and only 

 exerts 80 horfe-power ; a fingle afting engine of 66 inch, 

 and 60 horfe-power ; and two others of 64 and 60 inch, 

 equal to 51 and 54 horfe-power : — in the whole, 245 horfe- 

 power to drain one mine. 



The Dolcoath mine has three engines : a double engine 

 of 63 inch cylinder, and 132 horfe-power; a fingle engine 

 of 63 inch, and 45 horfe-power ; and a fmaller fingle engine 

 of 20 horfe-power : — in all, 197 horfe-power to drain the 

 mine. 



It will be obferved above, that the power of the different 

 engines is not in proportion to the dimenlions of the cyhn- 

 ders : this is becaufe the preflure upon each fquare inch of 

 the pifton varies in different engines from 7 to 20 pounds. 

 But cuilom has eftabliftied, that certain fizes of cyhnders 

 wiU be equal to a certain number of horfes' power, as is 

 (hewn by the following table. 



The fteam in the boiler is fuppofed to be kept within the 

 limits of from 2 to 4 lbs. preflure on each fquare inch more 

 than the atmofphere ; and in that cafe the cyhnders of the 

 diameters marked in the Table will have very nearly the 

 powers afligned to them. 



A Table 



