552 PHILOSOPHICAL TRANSACTIONS. |_ANNO 1722. 



is lifted up and down every stroke, and the water passes through dddd, the mer- 

 cury making a shell sometimes between the middle and inner cylinder, as in 

 the suction; and sometimes between the barrel and the middle cylinder, as in 

 the forcing stroke. 



Mr. Haskins had contrived such a machine as is represented by this 4th 

 figure, and bespoke the several parts before he died; and tlierefore when I was 

 desired by his assignees to direct the setting up the machine, I was obliged 

 to make use of the pieces already made, in order to save the expence of a new 

 engine: and now the whole put together with some alterations, make the en- 

 gine represented by fig. 5, as it is set up at my house in Westminster, and by 

 the force of one man, raises a hogshead of water in little more than a minute 

 and a half to the height of 27 feet. All the fault of the machine of fig. 5 is, 

 that the pendulum handle pf is too long, and the bottom of the middle cylinder c 

 ought to be just in the middle of the height to which the water is to be raised, 

 supposing three copper cylinders to be as they are here : if likewise the barrel 

 Dl d2 worked under the forcing pipe, the lift would be easier. Therefore I 

 describe the machine with the small alteration represented in fig. 6. 



The sucking and forcing pipe and valves are marked with the same letters as 

 in the other figures; and the chains e1 e2 must be supposed to hang from such 

 pullies, and to be moved by such a pendulum as in fig. 5. The barrel Dl d2, 

 otherwise called the outer cylinder, and represented by the same letters in 

 fig. 7, has within it another cylinder, called the inner cylinder or plug, as dddd 

 fig. 7, between which two cylinders a certain quantity of mercury is poured in, 

 and the hanging cylinder c coming down into the mercury, a stroke of 13 

 inches may be made by the motion of the barrel, which, in going down sucks 

 by making a vacuum in c, and in going up forces the water out of the top of 

 the forcing pipe, performing the office of a common piston; only that instead 

 of leather to make it tight to the cylinder c, there is always a thin shell of 

 quicksilver, either between the middle cylinder c and the inner one, dddd fig. 7, 

 as happens when the suction is made, or between the middle and outer cylinder, 

 as happens in lifting up the barrel to force. In the suction, the mercury is 

 higher in the inner shell than in the outer, by a height equal to little more 

 than -TT- part of the height of the barrel above the water to be raised : and in 

 forcing, it is higher in the outer shell than in the inner, by little more than 

 ^ of the height of the column of water to be forced. And therefore if the 

 water is not required to be raised above 64 feet, the barrel should move so as 

 to make the middle of its stroke at the height of 30 feet, or at the middle of 

 the way from the water to be raised, to the delivery at top. 



The 7 th figure, drawn by a larger scale, represents the three cylinders. 



