219

THE STEAM-ENGINE.

moment it is forced to part with this heat, it is turned back into the liquid form, or condensed.

In the above experiment, after the piston has been raised 1,700 inches, let the fire be removed, and cold water be applied to the surface of the tube. The latent heat will be abstracted, and the steam will be condensed and form once more a cubic inch of water at the bottom of the tube. As the steam condenses, successive vacuums are produced; and the piston, forced down by the pressure of the atmosphere, descends, and finally rests on the water as at first.

By applying heat again, the process may be repeated. An up-and-down motion may in this way be communicated to the piston; and the piston may be connected with machinery, which will thus be set in motion by the alternate evaporation of water and condensation of steam. This was the principle of the Atmospheric Engine, which was once extensively used, but has now been superseded.

The Steam-Engine.

558. HERO'S ENGINE.-Steam and some of its properties appear to have been known to the ancients centuries before the Christian era. Hero, of Alexandria, who flourished about 200 years B. C., has left us a description of a steam-engine by which machinery could be set in motion. Fig. 220 represents Hero's

Fig. 220.

able machinery connected with the band may be set in motion.

559. Hero's was a simple rotatory engine. No use was made of it for

how it may be condensed in the above experiment. What follows the condensation of the steam? How may an up-and-down motion be communicated to the piston? What engine was constructed on this principle? 558. How long ago was steam known? Who has left us a description of a steam-engine? Describe Hero's engine.

2,000 years; but the principle involved has been revived, and is applied in rotatory engines at the present day.

560. DE GARAY'S ENGINE.-In 1543, a Spaniard, by the name of De Garay, undertook to propel a vessel of 200 tons in the harbor of Barcelona by the force of steam. He kept his machinery a secret, but it was observed that a boiler and two wheels constituted the principal part of his apparatus. The experiment succeeded. The vessel moved three miles an hour, and was turned or stopped at pleasure; but the Emperor Charles V., by whose order the trial was made, never followed the matter up, and De Garay and his invention were forgotten.

561. ENGINES OF DE CAUS AND BRANCA.-In 1615, De Caus, a French mathematician, devised an apparatus by which water could be raised in a tube through the agency of steam. A few years afterwards, an Italian physician, named Branca, ground his drugs by means of a wheel set in motion by steam. The steam was led from a close vessel, in which it was prepared, and discharged against flanges on the rim of the wheel.

562. THE MARQUIS OF WORCESTER'S ENGINE.-The Marquis of Worcester, by many regarded as the inventor of the steam-engine, greatly improved on the imperfect attempts of those who had preceded him.

Some say that Worcester derived his ideas from De Caus. Others claim that his invention was purely original, and the result of reflections to which he was led during his imprisonment in the Tower of London, in 1656, for plotting against the government of Cromwell. Observing how the steam kept moving the lid of the pot in which he was cooking his dinner, he could not help thinking that this power could be turned to a variety of useful purposes, and set about devising an engine in which it might be applied to the raising of water.

The Marquis of Worcester generated his steam in a boiler, and led it by pipes to two vessels communicating on one side with the reservoir from which it was to be drawn, and on the other with the cistern into which it was to be discharged.

559. What sort of an engine was Hero's, and what is said of it? 560. Give an account of De Garay's engine, and the experiment made with it. 561. Give an account of De Caus's engine. Of Branca's. 562. Whom do many regard as the inventor of the steamengine? What claim has he to the honor? How was he led to reflect on the subject?

THE STEAM-ENGINE.

221

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. 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

A

No

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

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?

THE STEAM-ENGINE.

223

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

569. Describe the parts of Watt's Double-acting Condensing Engine. Show how the