coal, igniting that in turn, and, as claimed by Papin, the combustion was complete, and the formation of smoke was entirely prevented. He states, in "Acta Eruditorum," that the heat was intense, the saving of fuel very great, and that the only difficulty was to find a refractory material which would withstand the high temperature attained.

This is the first fire-box and flue boiler of which we have record. The experiment is supposed to have led Papin to suggest the use of a hot-blast, as practised by Neilson more than a century later, for reducing metals from their ores.

Papin made another boiler having a flue winding through. the water-space, and presenting a heating surface of nearly 80 square feet. The flue had a length of 24 feet, and was about 10 inches square. It is not stated what were the maximum pressures carried on these boilers; but it is known that Papin had used very high pressures in his digesters-probably between 1,200 and 1,500 pounds per square inch.

In the year 1705, Leibnitz, then visiting England, had seen a Savery engine, and, on his return, described it to Papin, sending him a sketch of the machine. Papin read the letter and exhibited the sketch to the Landgrave of Hesse, and Charles at once urged him to endeavor to perfect his own machine, and to continue the researches which he had been intermittently pursuing since the earlier machine had been exhibited in public.

In a small pamphlet printed at Cassel in 1707,' Papin describes a new form of engine, in which he discards the original plan of a modified Huyghens engine, with tightfitting piston and cylinder, raising its load by indirect action, and makes a modified Savery engine, which he calls the "Elector's Engine," in honor of his patron. This is the engine shown in the engraving, and as proposed to be used by him in turning a water-wheel.

I "Nouvelle manière d'élever l'Eau par la Force du Feu, mis en Lumière," par D. Papin. Cassel, 1707.

The sketch is that given by the inventor in his memoir. It consists (Fig. 18) of a steam-boiler, a, from which steam is led through the cock, c, to the working cylinder, n. The water beneath the floating-piston, h, which latter serves simply as a cushion to protect the steam from sudden condensation or contact with the water, is forced into the vessel rr, which

is a large air-chamber, and which serves to render the outflow of water comparatively uniform, and the discharge occurs by means of the pipe g, from which the water rises to the desired height. A fresh supply of water is introduced through the funnel k, after condensation of the steam in n, and the operation of expulsion is repeated.

This machine is evidently a retrogression, and Papin, after having earned the honor of having invented the first steam-engine of the typical form which has since become so universally applied, forfeited that credit by his evident ignorance of its superiority over existing devices, and by attempting unsuccessfully to perfect the inferior device of another inventor.

Subsequently, Papin made an attempt to apply the steam-engine to the propulsion of vessels, the account of which will be given in the chapter on Steam-Navigation.

Again disappointed, Papin once more visited England,

to renew his acquaintance with the savans of the Royal Society; but Boyle had died during the period which Papin had spent in Germany, and the unhappy and disheartened inventor and philosopher died in 1710, without having seen any one of his many devices and ingenious inventions a practical success.

CHAPTER II.

THE STEAM-ENGINE AS A TRAIN OF MECHANISM.

"THE introduction of new Inventions seemeth to be the very chief of all human Actions. The Benefits of new Inventions may extend to all Mankind universally; but the Good of political Achievements can respect but some particular Cantons of Men; these latter do not endure above a few Ages, the former forever. Inventions make all Men happy, without either Injury or Damage to any one single Person. Furthermore, new Inventions are, as it were, new Erections and Imitations of God's own Works."-BACON.

THE MODERN TYPE, AS DEVELOPED BY NEWCOMEN, BEIGHTON, AND SMEATON.

AT the beginning of the eighteenth century every element of the modern type of steam-engine had been separately invented and practically applied. The character of atmospheric pressure, and of the pressure of gases, had become understood. The nature of a vacuum was known, and the method of obtaining it by the displacement of the air by steam, and by the condensation of the vapor, was understood. The importance of utilizing the power of steam, and the application of condensation in the removal of atmospheric pressure, was not only recognized, but had been actually and successfully attempted by Morland, Papin, and Savery.

Mechanicians had succeeded in making steam-boilers capable of sustaining any desired or any useful pressure, and Papin had shown how to make them comparatively safe

by the attachment of the safety-valve. They had made steam-cylinders fitted with pistons, and had used such a combination in the development of power.

It now only remained for the engineer to combine known forms of mechanism in a practical machine which should be capable of economically and conveniently utilizing the power of steam through the application of now well-understood principles, and by the intelligent combination of physical phenomena already familiar to scientific investigators.

Every essential fact and every vital principle had been learned, and every one of the needed mechanical combinations had been successfully effected. It was only requisite that an inventor should appear, capable of perceiving that these known facts and combinations of mechanism, properly illustrated in a working machine, would present to the world its greatest physical blessing.

The defects of the simple engines constructed up to this time have been noted as each has been described. None of them could be depended upon for safe, economical, and continuous work. Savery's was the most successful of all. But the engine of Savery, even with the improvements of Desaguliers, was unsafe where most needed, because of the high pressures necessarily carried in its boilers when pumping from considerable depths; it was uneconomical, in consequence of the great loss of heat in its forcing-cylinders when the hot steam was surrounded at its entrance by colder bodies; it was slow in operation, of great first cost, and expensive in first cost and in repairs, as well as in its operation. It could not be relied upon to do its work uninterruptedly, and was thus in many respects a very unsatisfactory machine.

The man who finally effected a combination of the elements of the modern steam-engine, and produced a machine which is unmistakably a true engine—i. e., a train of mechanism consisting of several elementary pieces combined in a train capable of transmitting a force applied at one end