cylinders half filled with water, as well as the different diameters and depths of the said cylinders.

The table is extended to show the amount of water that can be raised by any number (from 1 to 90) of the largest of the above cylinders, each cylinder being 6 feet in diameter, 12 feet in length, and capable of raising 3240 lbs. weight of water.

He also gives the rate of the expansion of water when converted into steam at common atmospheric pressures, so nearly correct, that we may fairly conclude it to be the result of actual and careful experiment. The general character of his statement, and particularly his mention of the cannon, would lead us to conclude that the idea of his projected engine was borrowed from the Marquis' work, published twenty years before; but at all events, he is entitled to the merit of being the first accurate experimenter on the elastic force of steam.

The next practical application of steam power was made by Captain Savery (also an Englishman), who was the first to publish a method of producing a vacuum by the condensation of steam; and combining this with the elastic force employed by Worcester, he constructed an engine for raising water, for which he had letters patent granted in 1698; being the first patent on record for a steam engine. In 1699, he published a pamphlet, entitled "The Miner's Friend," in which he described his machine, several of which, according to Dr. Robison, had been erected previous to the patent being obtained. In June, the same year, he exhibited a model of his engine before the

members of the Royal Society, who were perfectly satisfied with the success attending his experiments.

It consisted of a furnace and boiler B (fig. 8); from the boiler two pipes, provided with cocks C, proceeded to two steam vessels S, which had branch pipes from a descending main D, and also to a rising main pipe A; each pair of branch pipes had valves a, b, to prevent the descent of the water raised by the condensation, or by the force of steam. Only one vessel S is shewn in the cut, the other being immediately behind it. One of the steam vessels being filled with steam, condensation was produced by projecting cold water from a small cistern E

against the vessel, and into the partial vacuum made by that means, the water by the pressure of the atmosphere was forced up the descending main D from a depth of about twenty feet; and on the steam being let into the vessels again, the valve b closed, and prevented the descent of the water; while the steam, having acquired force in the boiler, its pressure caused the water to raise the valve a, and ascend to a height proportional to the excess of the elastic force of the steam above the pressure of the air.

g, The guage cock for ascertaining the level of the water.

In subsequent engines, he employed only one steam vessel, and further improved his machine by the application of Papin's digester' or safety valve V, and making use of a small boiler to heat water for the large one, in order to prevent loss of time.

It is uncertain whether Savery was acquainted or not with the ideas of his predecessors. His claims to originality, and to the discovery of condensation, have been much questioned by Desaguliers, who also charges him with having bought up and destroyed all the copies of Worcester's book on which he could lay hands, in order to keep to himself the whole credit of the invention. This grievous charge, as Dr. Robison well observes, ought to be substantiated by very distinct evidence" yet Desaguliers produces none such; and he was too late to know what happened at the time." Besides, Savery's own account is so clear and distinct; such a liberal and honest appeal to experiment pervades the whole; and it is so free from the selfsufficiency and conceit too generally to be found in works of the kind, that we cannot help giving credit to his statement.

Under any circumstances, his original invention was considerable, and his machine very superior to that of the Marquis. To him is due the merit of the first use of condensation and the safety valve, the employment of a vessel to supply the boiler with hot water, and the use of the guage cock to ascertain the quantity of water in the boiler.

The defects of his machine were, great waste of steam from the cold vessel and cold fluid; and the machinery could not be

made available for mining purposes, as water could not be raised to a sufficient height without the use of such powerful steam as to become dangerous.

In 1690, Dr. Denys Papin, a French Protestant, first suggested using the alternate action of steam and air to produce motion. He proposed "turning a small surface of water into vapour by fire, applied to the bottom of the cylinder which contains it, which vapour forces up the plug or piston in the cylinder to a considerable height; and which, as the water cools, when taken from the fire, descends again by air's pressure, and is applied to raise water out of the mine”—a mode of operation so impracticable, that notwithstanding the aid he received from Libnitz, in prosecuting the idea, he was obliged to abandon his scheme. It appears that, in 1698, by command of Charles, Landgrave of Hesse (to whom he gives the credit of the first idea of a steam engine), he made several experiments, but without any useful result. Having seen an engraving of Savery's engine in 1705, he resumed his experiments, and published a tract on the subject in 1707; but notwithstanding his knowledge of what Savery had done, his most improved engines were incapable of performing more than had already been accomplished by Worcester.

His machine consisted of a boiler B (fig. 9), provided with a safety valve V, and a cylinder G H, connected to the boiler

by the steam pipe S. The cylinder was closed at the top, and contained a floating piston P; and the base of the cylinder terminated in a curved tube T, which ascended into a cylinder M; the bent tube had a pipe Y from a reservoir of water communicating with it, and it was provided with a valve at r. Now suppose the cylinder G H to be filled with cold water by the pipe Y from the reservoir, and the boiler to contain strong steam; by opening the cock E, the steam would be admitted, and pressing on the floating piston P, cause the water to ascend in the cylinder M; its return is prevented by the valve K, and the steam cock E being shut, and the cock R opened to let the condensed steam escape at the pipe R, the water from the reservoir refills the steam cylinder through the pipe Y, and is ready for repeating the operation. The water raised can be directed to any useful object by the pipe D.

He is principally famous as the inventor of the safety valve and the four-way cock, without the former of which, it is not improbable that steam would have been abandoned long ago as a most dangerous and ungovernable agent. Mankind are, moreover, considerably indebted to him for his proposal to use the joint powers of steam and air. This idea, when actually reduced to practice by Newcomen in his atmospheric engine, was productive of such favourable and beneficial effects, that the attention of scientific men was irresistibly attracted to steam power, and a course of experiments and investigations entered on, which otherwise they might never have been induced to attempt. Dr. Papin also suggested that the water raised by his engine might be used to turn a wheel, and so impel other machinery.

Amontons, a distinguished member of the French Academy of Sciences, presented to that body, in 1699, an account of an invention, which he calls a Fire Wheel, and which has induced most writers on the subject to place his name among the inventors of the steam engine; but the machine he describes can be considered as nothing but an air engine. He proposes, by the alternate application of fire and cold water, to cause an expansion and contraction of air, so as to produce motion.