ys Üf HydrmUi Engt Aes.

8 . The pressure of the atmosphere being equal to 1$ pounds uponevery square inch, it will be equal to about 12 pounds upon every cir-cular inch. So that if the bore of the syringe be round, and one inchin diameter, the piston will be prest down into it by a Force nearlyequal to 12 pounds: but if the bore be t wo inches diameter, the pistonwill be prest down with four times that for ce.

And hence it is eafy to find with what Force the atmosphere presses-upon any given number either of square or circular inches.

These being the principies upon which this engirie is constructed,we stiail next describe the chief working parts of it: which are, 1. Aboiler. 2. A cylinder and piston. 3. A beam or lever.

The boiler is a large vestel made of iron or eopperand commbnlyso big as to contain about 2000 gallons.

The cylinder is about 40 inches diameter, bored so smooth, and itsleathered piston fitting so dose, that little or no water can get betvveenthe piston and fides of the cylinder.

Things being thus prepared, the cylinder is placed upright, andthe fhank of the piston is fixed to one end of the beam , which turnson a center like a eommon balance.

The boiler is placed under the cylinder, with a eommunication be^tween them, which can be opened and Fhut occasionally.

The boiler is filled about half füll of water, and a strong fire ismade under it.* then, if the eommunication between the boiler and thecylinder be opened, the cylinder will be filled with hot steam ; whichwould drive the piston quite out at the top of it. But there is a Con-trivance by which the piston, when it is near the top of the cylinder,Fhuts the eommunication at the top of the boiler within.

This is no sooner shut, than another is opened, by which a littlecold water is thrown upwards in a jet into the cylinder, which mix-ing with the hot steam, condenses it immediately; by which means avacuum is made in the cylinder, and the piston is pressed down bythe weight of the atmosphere >, and so lifts up the loaded pump-rod atthe other end of the beam,

If the cylinder be 42 inches in diameter, the piston will be presseddown with a force greater than 20000 pounds, and will consequentlylift up that weight at the opposite end of the beam: and as the pump-rod with its piunger is fixed to that end, if the bore where theplunger works were 10 inches diameter, the water would be forcedup through a pipe of 180 yards perpendicular height

But, as the parts of this engine have a good deal of friction, andmust work with a considerable velocity, and there is no such thing2 as