(37.)

The failure of the engines proposed by Captain Savery in the work of drainage, from the causes which have been just mentioned, and the increasing necessity for effecting this object, arising from the large property in mines which became every year unproductive by being flooded, stimulated the ingenuity [Pg062] of mechanics to contrive some means of rendering those powers of steam exhibited in Savery's engine available.

Thomas Newcomen, the reputed inventor of the atmospheric engine, was an ironmonger, or, according to some, a blacksmith, in the town of Dartmouth in Devonshire. From his personal acquaintance and intercourse with Dr. Hooke, the celebrated natural philosopher, it is probable that he was a person of some education, and therefore likely to be above the position of a blacksmith. Being in the habit of visiting the tin mines in Cornwall, Newcomen became acquainted with the engine invented by Savery, and with the causes which led to its inefficiency for the purposes of drainage.

It has been stated that Papin, about the year 1690, proposed the construction of an engine working by the atmospheric pressure acting on one side of a piston against a vacuum produced by the condensation of steam on the other side. Papin was not conscious of the importance of this principle; for, so far from ever having attempted to apply it to practical purposes, he probably never constructed, even on a small scale, any machine illustrating it. On the contrary, he abandoned the project the moment he was informed of the principle and structure of the steam engine of Savery; and he then proposed an engine for raising water, acting by the expansive force of steam similar to Savery's, but abandoning the method of working by a vacuum.

This engine is described by Papin in a work published in 1707.

Fig. 13.

A ( fig. 13.) is an oval boiler, having a safety-valve B, which limits the pressure of the steam. It is connected with a cylinder C, by a curved pipe having a stop-cock at D. A pipe with a stop-cock G opens from the top of the cylinder into the atmosphere, and a safety-valve F is placed upon the cylinder. A hollow copper piston H moves freely in the cylinder, and floats upon the water. O is a funnel with a valve L in the bottom, opening downwards, through which the cylinder C may be filled with water to the level of the top of the funnel. A close air-vessel communicates with the cylinder C by the curved tube, and has a valve K opening upwards. The force-pipe through which the water is raised communicates [Pg063] with the air-vessel I. If the cock D be shut, and the cock G opened, water poured into the funnel O will rise into the cylinder C, the air which fills the cylinder escaping through the open pipe G. When the cylinder is thus filled with water, let the cock G be closed, and the cock D opened. The steam from the boiler, after heating the metal of the cylinder, will force the piston downwards, and drive the water through the curved tube into the vessel I, from which its return is prevented by the valve K, which is closed by its weight. The air which filled the vessel I will then be compressed, and by its elasticity will drive a column of water up the pipe N. After the contents of the cylinder have been thus discharged it may be refilled in the same manner, and the process repeated.

It will be perceived that this project is nothing more than a reproduction of the engine of the Marquis of Worcester. In the preface to the work containing this description, Papin gives an extract from a letter addressed by him to Leibnitz in 1698, from which it appears that he had abandoned his idea of working the piston by the atmospheric pressure acting against a vacuum, considering it to be a contrivance inferior [Pg064] to the engine now described. "We now raise water," he says, "by the force of fire, in a more advantageous manner than that which I had published some years before; for besides the suction, we now also use the pressure which the water exerts upon other bodies in dilating itself by heat; instead of which I before employed the suction only, the effects of which are more limited."

From documents which have been preserved in the Royal Society, it appears that Newcomen was acquainted with Papin's writings, and therefore probably first derived from them the suggestion which he subsequently realised in the atmospheric engine. Among some papers of Dr. Hooke's have been found notes for the use of Newcomen, on Papin's method of transmitting the force of a stream or fall of water to a distance by pipes. Hooke dissuaded Newcomen from attempting any machine on this principle, which, as first proposed by Papin, was impracticable. He exposed the fallacy of Papin's first project in several discourses before the Royal Society, and considered his improved edition of it, though free from fallacy, as impracticable.

Papin's project for producing a vacuum under a piston by condensing the steam having been published in the Actæ Eruditorum, in Latin, in 1690, and in French, at Cassel, in 1695, and subsequently, in the Philosophical Transactions, in England in 1697, cannot be supposed to be unknown to Dr. Hooke; and if known to him, would probably have been communicated to Newcomen. Dr. Hooke died in 1703, some years before the date of Newcomen's invention.

John Cawley, who was the associate of Newcomen in his experiments and inquiries, was a plumber and glazier of the same town. Newcomen and Cawley obtained a patent for the atmospheric engine in 1705, in which Savery was associated, he having previously obtained a patent for the method of producing a vacuum by the condensation of steam, which was essential to Newcomen's contrivance. It was not, however, until about the year 1711 that any engine had been constructed under this patent.

In the latter end of that year, according to Desaguliers, the patentees "made proposals to drain a colliery at Griff, in [Pg065] Warwickshire, in which work five hundred horses were constantly employed. This proposal not being accepted, they contracted, in the following March, to drain water for Mr. Back of Wolverhampton, where, after many laborious attempts, they succeeded in making their engine work; but not being either philosophers to understand the reason, or mathematicians enough to calculate the power and proportions of the parts, they very luckily, by accident, found what they sought for."

Fig. 14.

Newcomen resumed the old method of raising the water from the mines by ordinary pumps, but conceived the idea of working these pumps by some moving power less expensive than that of horses. The means whereby he proposed effecting this, was by connecting the end of the pump-rod D ( fig. 14.) by a chain with the arch head A of a [Pg066] working-beam A B, playing on an axis C. The other arch head B of this beam was connected by a chain with the rod E of a solid piston P, which moved air-tight in a cylinder F. If a vacuum be created beneath the piston P, the atmospheric pressure acting upon it will press it down with a force of fifteen pounds per square inch; and the end A of the beam being thus raised, the pump-rod D will be drawn up. If a pressure equivalent to the atmosphere be then introduced below the piston, so as to neutralise the downward pressure, the piston will be in a state of indifference as to the rising or falling; and if in this case the rod D be made heavier than the piston and its rod, so as to overcome the friction, it will descend, and elevate the piston again to the top of the cylinder. The vacuum being again produced, another descent of the piston, and consequent elevation of the pump-rod, will take place; and so the process may be continued.

Such was Newcomen's first conception of the atmospheric engine; and the contrivance had much, even at the first view, to recommend it. The power of such a machine would depend entirely on the magnitude of the piston; and being independent of highly elastic steam, would not expose the materials to the destructive heat which was necessary for working Savery's engine. Supposing a perfect vacuum to be produced under the piston in the cylinder, an effective downward pressure would be obtained, amounting to fifteen times as many pounds as there are square inches in the section of the piston.[12] Thus, if the base of the piston were 100 square inches, a pressure equal to 1500 pounds would be obtained.