coming from the end of the beam, so that t cannot turn on its axis, but must rise nd fall with the motion of the great beam.

A bar of iron connects the centres of the wo small toothed wheels; when therefore he beam raises the wheel 1, it must move round the circumference of the wheel н, and with it turn the fly-wheel x; which will make two revolutions while the wheel Igoes round it once. These are called the Sun and Planet wheels; H, like the sun, turns only on its axis, while I revolves about it as the planets revolve round the

sun.

If to the centre of the fly-wheel any machinery were fixed, the motion of the great beam Rs would keep it in constant work.

Charles. Will you describe the operations of the engine?

Father. Suppose the piston at the top of the cylinder, as it is represented in the plate, and the lower part of the cylinder filled with steam. By means of the pump

rod, EF, the steam valve a, and the eduction valve d will be opened together, the branches from which being connected at o. There being now a communication at d between the cylinder and condenser, the steam is forced from the former into the latter, leaving the lower part of the cylin der empty, while the steam from the boiler entering by the valve a presses upon the piston, and forces it down. As soon as the piston has arrived at the bottom, the steam valve c and the eduction valve b are opened, while those at a and d are shut; the steam, therefore, immediately rushes through the eduction valve b into the condenser, while the piston is forced up again by the steam, which is now admitted by the valve c.*

The author is obliged to Mr. Loway, engraver, and the proprietors of that interesting and useful periodical publication, entitled, "The Philosophical Ma gazine, comprehending the various Branches of Science," &c. &c. for the drawing of a steam-engine, which he has copied with some few alterations.

CONVERSATION XXXIX.

Of the Steam-Engine.

CHARLES. I do not understand how the two sets of valves act, which you described yesterday, as the steam and eduction valves.

Father. If you look to Fig. 36. Plate VIII. there is a different view of this part of the machine, unconnected with the rest : s is part of the pipe which brings the steam from the boiler, a represents the valve, which, being opened, admits the steam into the upper part of the cylinder, forcing down the piston.

Emma. Is not the valve dopened at the same time?

Father. It is: and then the steam which was under the piston is forced through into the condenser e. When the piston arrives at the bottom, the other pair of valves are opened, viz. c and b; through e the steam rushes to raise the piston, and through b the steam which pressed the piston down before, is driven out into the pipe r, leading to the condenser; in this there is a jet of cold water, constantly playing up, and thereby the steam is instantly reduced into the shape of hot water.

Charles. Then the condenser e (Fig. 35.) will soon be full of water.

Father. It would, if it were not con nected by the pipe z with the pump f: and every time the great beam R S is brought down, the plunger, at the bottom of the piston rod E F, descends to the bottom of the pump.

Emma. Is there a valve in the plunger?
Father. Yes, which opens upwards, con-

quently all the hot water which runs out the condenser into the pump, will escape rough the valve, and be at the top of the lunger, and the valve not admiting it to eturn, it will, by the ascent of the pistonod into the situation as is shown in the late, be driven through n into g, the cisern of hot water, from which, owing to a alve, it cannot return.

Charles. And I see the same motion f the great beam puts the pump y in acion, and brings over the hot water from he cistern g, through the pipe i i into the ittle cistern v, which supplies the boiler.

Emma. If the pump k brings in, by the ame motion the water from the well w, o not the hot and cold water intermix?

Father. No: if you look carefully in he figure, you will observe a strong partion v, which separates the one from the ther. Besides, you may perceive that he hot water does not stand at so high a vel as the cold, which is a sufficient proof hat they do not communicate. Indeed