VOL. XXXir.] PHILOSOPHICAL TRANSACTIONS. 553 



which are here made of copper in their just proportions: and for the sake of 

 those that would consider this matter fully, I have here given their lengths, 

 diameters within and without, and thickness. 



Inner Cylinder or plug closed at 

 Outer Cylinder or Barrel, Middle or hanging Cy- top by a Cap, and moving up 

 Dl D2. linder, in which the and down with the Barrel to 

 Stroke is made Ci C2 CO. which it is joined at bottom, 

 dddd. 

 Inches Inches Inches 



Length . . , 30 29.0 31.2 



Diameter within 6.74 6.35 6.03 



Thickness 0.10 0.08 0.13 



Diameter without 6,94' 6.51 6.29 



Here bb represents part of the elbow of fig. 5, or of the forcing pipe of fig. 6. 

 But as the spaces between the cylinders are so small, as not to be visible even 

 in a large draught made by a scale ; I have here given three more draughts of 

 the three cylinders, where the height is according to the scale of the 7th figure, 

 but the diameters of the middle and inner cylinders are made less than they are 

 in the engine, to make the space between, where the mercury rises and falls, 

 visible; and the cylinders themselves are represented by single lines. 



The quantity of mercury used in this engine, is 364- pounds, which being 

 poured in between the outer and inner cylinder, rises up to the height of 

 16 inches. 



When the barrel is pulled up, as in fig. 9, so as to have the middle cylinder 

 within an inch of the bottom of the barrel; the mercury on both sides the 

 middle cylinder will rise up to the height of 23.1 inches, that is about 2 inches 

 below the cup Dl, to the line qq. 



When the barrel is going down, to fill the sucking pipe and middle cylinder 

 c, the mercury in the inner shell will be 25 inches high, and only 13 in the 

 outer shell, fig. 9, where the shaded part represents the mercury. 



At the end of the sucking stroke the mercury is up to the top of the inner 

 cylinder, and scarcely an inch in the outer shell. Fig. 8. 



In raising the piston from forcing to sucking, the first I4- inch drives the 

 mercury out of the inner shell, and raises it in the outer 13.28 inches. 



The depth of an inch of water in the middle cylinder, above the inner one 

 or plug, is equal to a space in the outer shell of 13.28 inches, and 4- inch is 

 equal to the same height in the inner shell. 



Therefore, when the mercury is equally high in both shells, a motion of ^ 

 inch of the barrel will charge for suction. That is, on letting down the barrel 

 only i- inch, the pressure of the atmosphere in the outer shell will raise the 

 mercury in the inner, 13.28 inches, at the same time, that it pushes up the 

 water from the well 134^ feet high, into the sucking pipe. And when all the 



VOL. VI. 4 B 



