was condensed, and that the water rushed up into the flask to supply the vacuum caused by this condensation. This casual experiment is said to have given to Savery the idea of constructing an apparatus on this plan, for raising water. It also occurred to him, that he might employ the expansive power of steam, as used in De Caus' engine. All this he effected, and, by so doing, led the way for the brilliant inventions that were afterwards made in the construction of the steam-engine. This invention was principally devoted to raising water from mines, and bore the name of the "Miner's Friend;" "but," says M. Arago, in his life of James Watt, "the miners seemed scarcely to appreciate the important compliment he paid them. With one solitary exception, none of them ordered his machines." It appeared that, with all its advantages, this engine did not perform well. In 1705, Thomas Newcomen, a smith and ironmonger, and John Crawley, a plumber and glazier, both of Dartmouth in Devonshire, took out a patent for an improved machine, which they shared with Savery. The next improvement was made by a boy named Humphrey Potter, and arose from accident. M. Arago has thus described the circumstance:

"The first machine of Newcomen required the most unremitting attention on the part of the individual who unceasingly opened and closed certain stopcocks, first for the introduction of the steam into the cylinder, and then for injecting the cold shower for its condensation. It happened, on one occasion, that the person so em

ployed was a boy named Potter. His young companions, at their sports, uttered cries of delight, which vexed him beyond endurance. He was all impatience to join in their play; but his required duties did not allow him half-a-minute's absence. His anxiety excited his ingenuity, and led him to observe relations he had never before thought of. Of the two stopcocks, the one required to be opened at the moment that the beam (which Newcomen first and so usefully introduced into his machines) terminated the descending oscillation, and required to be closed precisely at the termination of the opposite one. The management of the other stopcock was precisely the reverse. The positions, then, of the beam, and of the stopcocks, had a necessary dependence upon each other. Potter seized upon this fact. He perceived that the beam might serve to impart to the other parts of the machine all the required movements; and on the moment he realized his conceptions. He attached a number of cords to the stopcocks, some to the one end of the handle, and some to the other, and these he attached to the most suitable parts of the beam, so that in ascending it pulled one set of the cords, and in descending, the other; and so effectually, that all the work of his hand was entirely superseded. For the first time the steam-engine went by itself; and now no other workman was seen near it but the fireman, who, from time to time, fed the furnace under the boiler. For the cords of young Potter, the engineers soon substituted rigid vertical rods, which were fixed

to the beam, and armed with small pegs, which either pressed from above downwards, or from below upwards, as required, and thus turned the different stopcocks and valves. These rods themselves have since been replaced by other combinations; but, however humbling the avowal, all these expedients are nothing more than simple modifications of a contrivance suggested to a child by his desire to join in the gambols of his youthful companions."

Such was the state in which the steam-engine was found by the great James Watt, at that time a mathematical instrument maker in Glasgow. There was in the museum of the university of that city a small model of one of Newcomen's steam-engines, which was used to instruct the students at college; but which could scarcely ever be made to work satisfactorily. Professor Anderson, who then filled the chair of Natural Philosophy, in the winter of 1763-4, requested Mr. Watt to repair it, which he soon did; but in doing so, the idea was suggested to him of an improvement in the condensing of the steam, and thus causing a great saving in the expense of the engine. The general practice at that period was to condense the steam in the same cylinder in which the piston works; but this cylinder being of cast iron, was, at every stroke, cooled nearly down to the temperature of the water employed to condense the steam, which caused a great quantity of heat to be wasted in again giving the cylinder the necessary temperature. After many trials, the fortunate thought occurred to Mr. Watt of saving all the

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waste of heat and fuel, by condensing the steam in a separate vessel, exhausted of air, and kept cool by injection, between which and the cylinder a communication was to be opened every time steam was to be condensed, while the cylinder itself was to be kept constantly hot; and having at last perfected this great improvement, (the separate vessel being called the "condenser,") a model was constructed, and the experiments made with it placed the correctness of the theory and the advantages of the invention beyond a doubt. This model has ever since been preserved among the apparatus of the university of Glasgow. His grand invention for saving steam and fuel in steam-engines was completed about the beginning of 1765; and in subsequent years he proceeded with his improvements, and introduced, among other discoveries, the rotatory motion of the sun and planet wheels, the expansive principle, the double engine, the parallel motion, and the smokeless furnace. The application of the centrifugal regulating force of "the governor" was another of his great practical improvements; and the perfection given to the rotative-engine soon led to its general application for imparting motion to almost every species of millwork and machinery. Thus, then, was the steam-engine completed, under the inventions, discoveries, and improvements of the great master-mind of James Watt.

THE STEAMBOAT.

THE parent idea of steam navigation, doubtless, took its rise in the latest attempts at superseding sails and oars by the use of "mill-work," to move ships and boats against adverse winds, and opposing tides and

currents. Such efforts were begun many ages ago, and not relinquished till near the close of the eighteenth century.

In the year 1730, one Dr. John Allen, in a pamphlet detailing some experiments of his own in mechanics, expressed his belief, that if a couple of fire (that is, steam) engines were applied to a ship of fourteen hundred or fifteen hundred tons, they would impel it at the rate of three knots an hour. But to Jonathan Hulls the honour is due, not only of suggesting the possibility of such things, but also of having embarked his means in their realization, by a series of costly experiments, on the faith of which he took out a patent, dated Dec. 21, 1736. Unhappily, Hulls was not able to realize his project himself; neither does it appear that any one stepped forward to help him.

In the year 1774, Count d'Auxiron experimented with some kind of a steamboat upon the Seine, near Paris; but his engine was weak, and a failure ensued. Monsieur J. C. Perier, a superior practical machinist, was present on the foregoing occasion, and noted, as he supposed, such defects as could easily be remedied.