While the engine was still in its trial state, a curious accident occurred which led to another change in the mode of condensation, and proved of essential importance in establishing Newcomen’s engine as a practicable working power. The accident was this: in order to keep the cylinder as free from air as possible, great pains were taken to prevent it passing down by the side of the piston, which was carefully wrapped with cloth or leather; and, still further to keep the cylinder air-tight, a quantity of water was kept constantly laying on the upper side of the piston. At one of the early trials the inventors were surprised to see the engine make several strokes in unusually quick succession; and on searching for the cause, they found it to consist in a hole in the piston, which had let the cold water in a jet into the inside of the cylinder, and thereby produced a rapid vacuum by the condensation of the contained steam. A new light suddenly broke upon Newcomen. The idea of condensing by injection of cold water directly into the cylinder, instead of applying it on the outside, at once occurred to him; and he proceeded to embody the expedient which had thus been accidentally suggested, as part of his machine. The result was the addition of the injection-pipe, through which, when the piston was raised and the cylinder was full of steam, a jet of cold water was thrown in, and the steam being suddenly condensed, the piston was at once driven down by the pressure of the atmosphere.
An accident of a different kind shortly after led to the improvement of Newcomen’s engine in another respect. To keep it at work, one man was required to attend the fire, and another to turn alternately the two cocks, one admitting the steam into the cylinder, the other admitting the jet of cold water to condense it. The turning of these cocks was easy work, usually performed by a boy. It was, however, a very monotonous duty, though requiring constant attention. To escape the drudgery and obtain an interval for rest, or perhaps for play, a boy named Humphrey Potter, who turned the cocks, set himself to discover some method of evading his task. He must have been an ingenious boy, as is clear from the arrangement he contrived with this object. Observing the alternate ascent and descent of the beam above his head, he bethought him of applying the movement to the alternate raising and lowering of the levers which governed the cocks. The result was the contrivance of what he called the scoggan,[43] consisting of a catch worked by strings from the beam of the engine. This arrangement, when tried, was found to answer the purpose intended. The action of the engine was thus made automatic; and the arrangement, though rude, not only enabled Potter to enjoy his play, but it had the effect of improving the working power of the engine itself; the number of strokes which it made being increased from six or eight to fifteen or sixteen in the minute. This invention was afterwards greatly improved by Mr. Henry Beighton, of Newcastle-on-Tyne, who added the plug-rod and hand-gear. He did away with the catches and strings of the boy Potter’s rude apparatus, and substituted a rod suspended from the beam, which alternately opened and shut the tappets attached to the steam and injection cocks.
NEWCOMEN’S ENGINE.[44]
Thus, step by step, Newcomen’s engine grew in power and efficiency, and became more and more complete as a self-acting machine. It will be observed that, like all other inventions, it was not the product of any one man’s ingenuity, but of many. One contributed one improvement, and another another. The essential features of the atmospheric engine were not new. The piston and cylinder had been known as long ago as the time of Hero. The expansive force of steam and the creation of a vacuum by its condensation had been known to the Marquis of Worcester, Savery, Papin, and many more. Newcomen merely combined in his machine the result of their varied experience, and, assisted by the persons who worked with him, down to the engine-boy Potter, he advanced the invention several important stages; so that the steam-engine was no longer a toy or a scientific curiosity, but had become a powerful machine capable of doing useful work.
The comparative success which attended the working of Newcomen’s first engine at the colliery near Wolverhampton, shortly induced other owners of coal-mines to adopt it. There were great complaints in the north, of the deeper mines having become unworkable. All the ordinary means of pumping them clear of water had failed. In their emergency, the colliery-owners called Newcomen and Calley to their aid. They were invited down to Newcastle-upon-Tyne, in the neighbourhood of which town they erected their second and third engines. They were next summoned to Leeds, and erected their fourth engine at Austhorpe, in 1714. It was the sight of this engine at work which first induced Smeaton, when a boy, to turn his attention to mechanics, and eventually led him to study the atmospheric-engine, with a view to its improvement. The cylinder of the engine erected at Austhorpe, like those which had preceded it, was about 23 inches in diameter, and made about fifteen strokes a minute. The pumps, which were in two lifts, and of 9 inches bore, drew the water from a depth of 37 yards. The patentees had 250l. a year for working and keeping the engine in order. Calley superintended its erection, and afterwards its working; but he did not long survive its completion, as he died at Austhorpe in 1717.
The next engines were erected by Newcomen in Cornwall, where there was as great a demand for increased pumping-power as in any of the collieries of the north. The first of Newcomen’s construction in Cornwall was erected in 1720, at the Wheal Fortune tin mine, in the parish of Ludgvan, a few miles north-east of Penzance. The mine was conducted by Mr. William Lemon, the founder of the fortunes of the well-known Cornish family. He was born in a humble station in life, from which he honourably raised himself by his great industry, ability, and energy. He began his career as a mining-boy; was at an early age appointed one of the managers of a tin-smelting house at Chiandower, near Penzance; and after the experience gained by him in that capacity he engaged in the working of the Wheal Fortune mine. With the help of Newcomen’s engine, the enterprise proved completely successful; and after realising a considerable sum he removed to Truro, and began working the great Gwennap mines on such a scale as had never before been known in Cornwall.[45]
The Wheal Fortune engine was on a larger scale than any that had yet been erected, the cylinder being 47 inches in diameter, making about fifteen strokes a minute. It drew about a hogshead of water at each stroke, from a pump 30 fathoms deep, through pit-barrels 15 inches in diameter, and its performances were on the whole regarded as very extraordinary. The principal objection to its use consisted in the very large quantity of coal that it consumed and the heavy cost of maintaining it in working order. There was a great waste, especially in boilers, the making of which was then ill understood. Smeaton relates that in the course of four years’ working of the first Austhorpe engine, not fewer than four boilers were burnt out. The Wheal Fortune engine, however, answered its purpose. It kept down the water sufficiently to enable Mr. Lemon to draw up his tin, and on leaving the mine, he took with him to Truro a clear sum of ten thousand pounds. The engine-house is now in ruins, and presents a highly picturesque appearance, as seen from the heights of Trewal, reminding one of a Border Peel rather than of a mining engine-house.
RUINS OF WHEAL FORTUNE.