It should be added, that after the machine begins to work, and the water has risen into and filled the force-pipe, it fills also a little cistern, and by that means fills another pipe, called the condensing-pipe, which may be turned either way, over any of the receivers, when either is thoroughly heated by, the steam, to condense it within, thereby producing a vacuum, which absorbs the water out of the well into the receiver, on the principle of a syphon. Also a little above the cistern goes another pipe to convey the water from the force-pipe into the lesser boiler, for the purpose of replenishing the great boiler, when the water in it begins to be almost consumed. Whenever there is occasion for this, the cock is to be turned which communicates between the force-pipe and the lesser boiler, to close it effectually; at the same time having put a little fire beneath the small boiler, which will grow hot; its own steam, which has no vent to escape, pressing on its surface, will force the water up another pipe, through an aperture in the great boiler, and so long will it run, till the surface of the water gets so low as to be beneath the bottom of the pipe of communication—then the steam and water running together, will cause the valve (called a clack) to strike, which will intimate to the operator that it has discharged itself into the greater boiler, and carried in as much water as is then necessary; after which, by turning a cock, as much fresh water is let in as may be necessary; and then, by turning another cock, new fresh water is let out of a recipient into the less boiler as before; and thus the engine is supplied without fear of decay, or any delay in the operations; and proper attention in the workmen is only necessary to prevent disorder in a machine so expensive and complicated.
Also, to know when the great boiler wants replenishing, turn the gauge-cock; if water comes out, it does not need a supply; but if steam alone, then the want of water is certain. The like with the cock with which the lesser boiler is prepared for the same purpose, when the same state will be marked by like results. In working this engine, very little skill, and less labour is required: Attention is the chief requisite; it is only to be injured by want of due care, extreme stupidity, or wilful neglect.
The engine described above, does not differ essentially from that first designed by the inventor, Captain Savery; the chief alteration which now occurs, is only in some few slight particulars. For example, the original engine had only one boiler, and there was no ready means for supplying it with water, to remedy the waste occasioned by evaporation of steam, without stopping the action of the engine, whenever the boiler was emptied to such a degree as to risk burning the vessel. After it was replenished the machine had to remain idle till the steam was raised, thus causing an immense loss of time; which is remedied by the application of a second boiler.
The description of the engine formerly mentioned is transcribed from Mr. Savery’s publication, “The Miner’s Friend,” and which had a subsidiary boiler, with water of a boiling heat, always ready to supply the large boiler; and the power of steam raised in it is employed to force the water into the larger boiler, to replace the waste occasioned by evaporation from that boiler; by this means the transposition of the feeding water is not only speedily performed, but being itself of a boiling heat, it is instantly ready to produce steam for carrying on the work. There is also one more grand improvement in the modern machine: the first engine was worked by four separate cocks, which the operator was compelled to turn separately at every change of stroke; if he turned them wrong, he was not only liable to damage the engine, but he prevented its effect, and, at the same time, lost a part of the operation: whereas, in the improved engine, the communications are made by a double sliding valve, or, as it has since been termed, regulator; that is, a brass plate, shaped like a fan, and moving on a centre within the boiler, so as to slide horizontally in contact with the under surface of the cover of the boiler, to which it is accurately fitted by grinding, and thus, at pleasure, opens or shuts the orifices, or entries, to the steam pipes of the two receivers alternately. This regulator acts with less friction than a cock of equal bore, and, by the motion of a single handle backwards, at once opens the proper steam pipe from one receiver, and closes that which belongs to the other receiver. Captain Savery, in his publication before noticed, describes the uses to which this machine may be applied, besides those before described, viz.—1, to serve water for turning all sorts of mills; 2, for supplying palaces, noblemen and gentlemen’s houses with water, and affording the means for extinguishing fires therein, by the water so raised; 3, the supplying cities and towns with water; 4, draining fens and marshes; 5, for ships; 6, for draining mines of water; and 7, for preventing damps in mines.
Dr. Desaguliers, we conceive, ungenerously attacked Captain Savery’s reputation, by alleging that this was not an original invention, and that he was indebted for the first idea to the previously mentioned plan of the Marquis of Worcester. Dr. Rees, with a generous liberality worthy his great critical discrimination, scientific skill, and general erudition, has, we think, ably defended the captain’s character, by proving his ideas to have originated with himself; we have only an opportunity to notice the most prominent features in this justification, where Dr. Rees thus expresses himself. “We know that the Marquis of Worcester gave no hint concerning the contractibility or condensation of steam, upon which all the merit of the modern engine depends. The Marquis of Worcester’s engine was actuated wholly by the elastic power of steam, which he either found out, or proved by the bursting of cannon in part filled with water; and not the least hint that steam so expanded, is capable of being so far contracted in an instant, as to leave the space it occupied in a vessel, and occasion, in a great measure, a vacuum.”
Subsequent to the Marquis of Worcester’s, and Captain Savery’s original ideas, and also, subsequent to the perfection the captain had brought his machine to, M. Amonton, a native of France, invented a machine which he called a fire-wheel; but it does not appear that it was ever brought to that perfection to be conducive to real utility, although it was certainly very ingenious.
Also, M. Papin, a native of Germany, made some pretensions to what he alleged was an invention of his own, only it happened to appear, unfortunately for his claim, that he was in London, and present at the time when Captain Savery exhibited the model of his steam-engine to the Royal Society. He made some unsuccessful experiments, by order of his patron, the Landgrave of Hesse, which sufficiently proved that, if he was the inventor, he did not understand the nature of his own machine.
Not long after Savery had invented his engine, Thomas Newcomen, an ironmonger, and John Calley, a glazier, began to direct their attention to the employment of steam as a mechanic power. Their first engine was constructed about the year 1711. This machine still acted on the principle of condensing the steam by means of cold water, and the pressure of the atmosphere on the piston. It was found of great value in pumping water from deep mines; but the mode of its construction, the great waste of fuel, the continued cooling and heating of the cylinder, and the limited capacities of the atmosphere in impelling the piston downward, all tended to circumscribe its utility.
The steam-engine was in this state, when it happily attracted the attention of Mr. Watt, to whom the merit and honour is due, of having first rendered this invention available as a mechanical agent. We cannot illustrate the improvements of this ingenious individual better than by giving a short biographical sketch of him to whom the world is so much indebted.
James Watt was born at Greenock, an extensive seaport in the west of Scotland, on the 19th of January, 1736. His father was a merchant, and also one of the magistrates of that town. He received the rudiments of his education in his native place; but his health being then extremely delicate, as it continued to be to the end of his life, his attendance at school was not always very regular. He amply made up, however, for what he lost in this way, by the diligence with which he pursued his studies at home, where, without any assistance, he succeeded, at a very early age, in making considerable proficiency in various branches of knowledge. Even at this time it is said his favourite study was mechanical science, to a love of which he was probably in some degree led by the example of his grandfather and his uncle, both of whom had been teachers of mathematics, and had left a considerable reputation for learning and ability in that department. Young Watt, however, was not indebted to any instruction of theirs for his own acquirements in science, the former having died two years before, and the latter one year after he was born. At the age of eighteen he was sent to London, to be apprenticed to a maker of mathematical instruments; but in little more than a year the state of his health forced him to return to Scotland; and he never received any further instruction in his profession. A year or two after this, however, a visit which he paid to some relations in Glasgow, suggested to him the plan of attempting to establish himself in that city, in the line for which he had been educated. In 1757, he accordingly removed thither, and was immediately appointed mathematical instrument maker to the College. In this situation he remained for some years, during which, notwithstanding almost constant ill health, he continued both to prosecute his profession, and to labour in the general cultivation of his mind, with extraordinary ardour and perseverance. Here also he enjoyed the intimacy and friendship of several distinguished persons, who were then members of the University, especially of the celebrated Dr. Black, the discoverer of the principle of latent heat, and Dr. Robison, so well known by his treatises on mechanical science, who was then a student, and about the same age as himself. Honourable, however as his present appointment was, and important as were many of the advantages to which it introduced him, he probably did not find it a very lucrative one; and therefore, in 1763, when about to marry, he removed from his apartments in the University, to a house in the city, and entered upon the profession of a general engineer.