VOL. XXXVII.] PHILOSOPHICAL TRANSACTIONS. /145 



When the river is at best, the wheels go 6 times round I ^ 

 in a minute, and but 44- at middle water 5 



The number of strokes in a minute 684 



The stroke 2i feet, in a 7 inch bore, raises 3 



ale 

 gallons 



They raise per minute 2052 

 That is, 123120 gallons = 1954 hogsheads per hour, and at the rate of 

 46896 hogsheads in a day, to the height of 120 feet. 



This is the utmost quantity they can raise, supposing there were no imper- 

 fections or loss at all. 



But it is certain from the following considerations, that no engine can raise 

 so much, as will answer the quantity of water the cylinder contains, in the 

 length of the forcer, or piston's motion: for, 1. The opening and shutting of 

 the valves lose nearly so much of that column, as the height they rise and fall. 



2. No leather is strong enough for the piston; but some water must conti- 

 nually slip or squeeze by, when it is raised to a considerable height; and when 

 the column is short, it will not press the leather enough to the cylinder, or 

 barrel; but especially at the beginning, or first moving of the piston, there is 

 so little weight on it, that before the leather can expand, there is some loss. 



3. And this loss is more or less, as the pistons are looser or tighter leathered. 



4. When the leathers grow too soft, they are not capable of sustaining the 

 column to be raised. 5. If they be leathered very tight, so as to lose no water, 

 then a great part of the engine's force is destroyed by the friction. 



By some experiments Mr. Beighton accurately made on engines, whose parts 

 are large and very well executed, they will lose 4- and sometimes ^ of the cal- 

 culated quantity. However the perfections or errors of engines are to be com- 

 pared together by the calculated quantities or forces; for, as they differ in 

 those, they will proportionably differ in their actual performances. 



The power by which the wheels are moved, is as follows. 



The weight of the column of water on a forcer 7 inches in diameter, and 

 120 feet high. 



7 X 7 = 49 lb. the pounds aver, in a yard nearly 

 40 yards high 



i960 lb, on one forcer 

 8 forcers always lifting 



Ihe whole weight on 1 



the engine at once . . \ ^^^^^ ^^- = ^"^^ '^^^ = 7 ^on weight. 



