563. PAPIN'S ENGINE.--The next step was taken by Papin, who devised the mode of giving a piston an up-anddown motion in a cylinder by alternately generating and condensing steam below a piston.

564. SAVERY'S ENGINE.-Captain Thomas Savery, in 1698, constructed an engine superior to any before invented. He was led to investigate the subject by the following occurrence. Having finished a flask of wine at a tavern, he flung it on the fire, and called for a basin of water to wash his hands. Some of the wine remained in the flask, and steam soon began to issue from it. Observing this, Savery thought that he would try the effect of inverting the flask and plunging its mouth into the basin of cold water. No sooner had he done this than the steam condensed, and the water rushing into the flask nearly filled it. Confident that he could advantageously apply this principle in machinery, Savery rested not till he invented an engine which was employed with success in drawing off the water from mines.

D

Fig. 221.

I

B

A

565. The principle on which Savery's engine worked, may be understood from Fig. 221. S is a pipe connecting a boiler in which steam is generated (and which does not appear in the Figure) with a cylindrical vessel, C, called the receiver. I is known as the injection-pipe, and is used for throwing cold water into the receiver to condense the steam. The steam-pipe, S, and the injection-pipe, I, contain the stop-cocks, G, B, which are moved by the common handle, A, so arranged that when one is opened the other is closed. F is a pipe which descends to the reservoir whence the water is to be drawn, and is commanded by the valve V, opening upward. ED is a pipe leading from the bottom of the receiver up to the cistern, into which the water is to be discharged. This pipe contains the valve Q, opening upward.

E

F

Operation. To work the engine, open the stop-cock G, which of course involves the shutting of B. The steam rushes in through S, and fills the receiver C, driving out the air through the valve Q. When C is full, shut G

How was the Marquis of Worcester's apparatus arranged? 563. Who took the next step? What was Papin's improvement? 564. Who constructed a superior engine in 1698? Relate the circumstances that led Savery to investigate the subject. 565. With the aid of Fig. 221, describe the parts of Savery's engine. Explain its operation.

and open B. Cold water at once enters through the injection-pipe and condenses the steam in C. A vacuum is thus formed, and the water in the reservoir or mine, under the pressure of the atmosphere, forces open the valve V, and rushes up through Finto G, till the receiver is nearly filled. G is then opened and B closed; when the steam again enters through S, and by its expansive force opens the valve Q, and drives the water up through ED into the cistern.

566. NEWCOMEN'S ENGINE.-Savery's engine was employed only for raising water; but Newcomen, an intelligent blacksmith, extended its sphere of usefulness, by connecting a piston, worked up and down on Papin's principle, with a beam turning on a pivot, by means of which machinery of different kinds could be set in motion.

m the

567. About this time, also, the engine was made self-acting through the ingenuity of Humphrey Potter, a lad employed to turn the stop-cocks Preferring play to this monotonous labor, he contrived to fasten cords beam to the handle of the stop-cocks, in such a way that the latter were opened and closed at the proper times, while he was away, enjoying himself with his companions. His device was after a time found out, and saved so much labor that it was at once adopted as an essential part of the machine.

568. WATT'S ENGINE.-The genius of James Watt brought the steam-engine to such perfection that but little improvement has since been made in it. Gifted with remarkable mathematical powers and a reflective mind, he commenced his experiments in 1763. Having been employed to repair one of Newcomen's engines, he soon perceived that there was a great loss in consequence of having every time to cool down the receiver from a high degree of heat before the steam could be condensed. This difficulty he remedied by providing a separate chamber called a condenser, to which the steam was conveyed and in which it was condensed. He also made the movement of the piston more prompt and effective by introducing steam into the cylinder alternately above and below it. The Doubleacting Condensing Steam-engine, as improved by Watt, and

566. What was the only purpose for which Savery's engine was employed? Who extended its usefulness, and how? 567. Give an account of Humphrey Potter's improvement, and the circumstances under which it was devised. 568. Who brought the steam-engine to comparative perfection? When did Watt commence his experiments? What disadvantage did he perceive that Newcomen's engines labored under? How did he remedy the difficulty? What other improvement did he make?

now generally constructed for manufacturing establishments, is represented in Fig. 222.

569. Description of the Parts.-A is the cylinder, in which the piston T works. This piston is connected by the piston-rod R with the working-beam

THE DOUBLE-ACTING CONDENSING STEAM-ENGINE.

V W, which turns on a pivot, U. The other end of the working-beam, O, imparts a rotary motion to the heavy fly-wheel X Y, by means of the connecting-rod P and the crank Q. The fly, as explained on page 125, regulates the motion, and is directly connected with the machinery to be moved. Steam

is conveyed to the cylinder A from the boiler (which is not seen in the figure), through the steam-pipe B, which is commanded by the throttle-valve C. This valve is connected with the governor D, in such a way as to be opened when the supply of steam is too small and closed when it is too great.

Communicating with the cylinder at its top and bottom on the left, are two hollow steam-boxes, E, E, each of which is divided into three compartments by two valves. F is called the upper induction-valve, and opens or closes communication between the steam-pipe and the upper part of the cylinder, so as to admit or intercept a supply of steam. G, called the upper exhaustionvalve, opens or closes communication between the upper part of the piston and the condenser K, so that the steam may either be allowed to escape into the latter or confined in the cylinder. The lower induction-valve g, and the lower exhaustion-valve f, stand in the same relation to the lower part of the cylinder, the former connecting it with the steam-pipe, and the latter with the condenser K. These valves are connected by a system of levers with a common handle, H, called a spanner, which is made to work at the proper intervals by a pin projecting from the rod L, which is moved by the workingbeam. The spanner works so as to open and close the valves by pairs. When it is pressed up, it opens F and ƒ, and closes G and g; when pressed down, it closes F and ƒ and opens G and g.

Below is the condensing apparatus, consisting of two cylinders, I and J, immersed in a cistern of cold water. A pipe, K, having an end like the rose of a watering-pot, conveys water from the cistern to the cylinder I (the supply being regulated by a stop-cock), and thus condenses the steam which is from time to time admitted into I. The other cylinder, J, called the air-pump, contains a piston with a valve in it opening upward, which works like the bucket of a common pump, and draws off the surplus water that collects at the bottom of the cylinder I into the upper reservoir S. The hot-water pump M then conveys this water to the cistern that supplies the boiler. To keep the water around the condensing apparatus at the right temperature, a fresh supply is constantly introduced through the cold-water pump N; which, like the hot-water pump and the air-pump, is kept in operation by rods connected with the working-beam.

570. Operation. The working of the engine is as follows:-Let the piston be at the top of the cylinder, and all the space below be filled with steam. The upper induction-valve and the lower exhaustion-valve are then opened by the spanner, while the upper exhaustion-valve and the lower inductionvalve are closed. By this means steam is introduced above the piston, while the steam beneath is drawn off into the condenser, where it is converted into water. The pressure of the steam above at once forces the piston to the bottom of the cylinder. Just at this moment the spanner is moved in the opposite direction, and the valves that were before opened are closed, while those that were previously closed are opened. The steam is now admitted beneath the piston, and the steam above is drawn off into the condenser and converted into water as before. While this action is going on, the cold-water pump

valves work. Describe the condensing apparatus. 570. How is the engine worked?

is constantly supplying the cistern in which the condenser is immersed; while the air-pump is drawing off the hot water from the condenser to the upper reservoir, whence it is conveyed by the hot-water pump to the cistern that supplies the boiler. An up-and-down motion is thus communicated to the piston, and by it to the working-beam, which causes the fly to revolve, and moves the machinery with which it is connected.

571. The Governor.-The Governor, an ingenious piece of mechanism, by which the throttle-valve in the steampipe is opened and closed, and the supply of steam regulated as the machinery requires, is worthy of further description.

H

Fig. 223.

E

The governor and its connection with the throttle-valve are represented in Fig. 223. It consists of two heavy balls of iron, E, E, suspended by metallic arms from the point e. At e they cross, forming a joint, and are continued to f,f, where they are attached by pivots to other bars, fh,fh. These bars are joined to one end of a lever, the other end of which, H, is connected at W with the handle of the valve Z. The spindle DD, to which the balls are attached, turns with the fly-wheel. When the fly-wheel revolves very rapidly, the balls E E, under the influence of the centrifugal force, fly out from the spindle, and with the aid of the bars fh,ƒh, pull down the end of the lever g. The other end, H, is of course raised, and with it the handle of the valve Z, which is thus made to close the mouth of the steam-pipe A and cut off the supply of steam. On the other hand, when the motion of the fly diminishes, the centrifugal force of the balls E E also diminishes, and they fall towards the spindle. The nearer end of the lever g is thus raised, while the end H is depressed. The valve Z is by this means opened, and admits a full supply of steam. The governor thus acts almost with human intelligence, now admitting, and now cutting off the steam, just as is required.

THE GOVERNOR.

572. The Boiler.-The boiler is made of thick wroughtiron or copper plates, riveted as strongly as possible, so as to resist the expansive force of the steam generated within.

How are the cisterns supplied? 571. What is the Governor? Describe the governor, and its connection with the throttle-valve. Show the workings of the gov