^S^ CALCULATIONS for 



receiver to the height of 30 feet only inflead of 34 feet, we fliall 

 by this means allow about 4 feet for the imperfeftion of the va- 

 cuum, or nearly one-eighth part of the whole power of the ma- 

 chine, if the (team in the receiver could be perfectly condenfed. 

 Let therefore the higheft elevation of the water in the receiver 

 be 24 feet above the furface of the water in the refervoir, and 

 if the bottom of the receiver and the upper part of the ciflern 

 or penftock be each 20 feet above the fame level, the diameter 

 of the water-wheel may be eafjly afcertained when the depth of 

 the penftock or head of water is given. 



Now as the velocity of the water is continually retarded dur- 

 ing the time employed to fill the receiver, we muft again have re- 

 courfe to the inverted fyphon (Fig. 2.) in order to determine 

 the time in which it may be filled and emptied, which when af- 

 certained, we fliall be enabled to calculate the number of ftrokes 

 the iTiachine may make in a minute, and confequently the quan- 

 tity of water it will deliver on any overfliot water-wheel in a given 

 time. 



The example on page 355 was purpofely intended tofliewthc 

 time neceflary for filling the receiver according to the above dimen- 

 iions, where ^=30, ^'=24, r=2o and c=4 feet ; whence it ap- 

 pears that it may be filled in o'.Sg to an height of 4 feet above 

 its bottom, or 24 feet above the level of HHH. 



The common iteam-engine invented by Newcomen and Caw- 

 iey, when it works to the beft advantage, requires the fteam to 

 be made about one-tenth ftronger than the furrounding air ; but 

 that this receiver may be emptied with fufficient difpatch, it will 

 be neceflary to increafe the elafticity of the fteam at leaft one- 

 fourth part beyond what is produced from the ufual heat of 

 boiling water. Admitting therefore that a column of water 34 

 feet in height be in equilibrio with the preflfure of the atmof- 



phere, we have M=8.5 feet, which added to 24, the highefl: 



4 

 elevation of the water above the furface of that in the refervoir, 

 gives 32.5 for the fpace AB. Fig. 2. There being now but a 

 column of 24 feet inftcad of 30 as before, prefTmg againft a 

 countcrafting column of 20 feet, the defcent of the water in 

 the receiver will be confiderably flower than its afcent, during 

 the time occupied in filling it to an height of 4 feet above its 



bottom ; 



