Stories of Invention, Told by Inventors and their Friends

by Edward Everett Hale

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 (meaning presumably the loafer or lazy boy), 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 afterward 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.

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.

JAMES WATT AND THE STEAM-ENGINE.

It was in the year 1759 that Robison[9] first called the attention of his friend Watt to the subject of the steam-engine. Robison was then only in his twentieth, and Watt in his twenty-third year. Robison's idea was that the power of steam might be advantageously applied to the driving of wheel-carriages; and he suggested that it would be the most convenient for the purpose to place the cylinder with its open end downwards to avoid the necessity of using a working-beam. Watt admits that he was very ignorant of the steam-engine at the time; nevertheless, he began making a model with two cylinders of tin plate, intending that the pistons and their connecting-rods should act alternately on two pinions attached to the axles of the carriage-wheels. But the model, being slightly and inaccurately made, did not answer his expectations. Other difficulties presented themselves, and the scheme was laid aside because Robison left Glasgow to go to sea. Indeed, mechanical science was not yet ripe for the locomotive. Robison's idea had, however, dropped silently into the mind of his friend, where it grew from day to day, slowly and at length fruitfully.

At his intervals of leisure and in the quiet of his evenings, Watt continued to prosecute his various studies. He was shortly attracted by the science of chemistry, then in its infancy. Dr. Black was at that time occupied with the investigations which led to his discovery of the theory of latent heat, and it is probable that his familiar conversations with Watt on the subject induced the latter to enter upon a series of experiments with the view of giving the theory some practical direction. His attention again and again reverted to the steam-engine, though he had not yet seen even a model of one. Steam was as yet almost unknown in Scotland as a working power. The first engine was erected at Elphinstone Colliery, in Stirlingshire, about the year 1750; and the second more than ten years later, at Govan Colliery, near Glasgow, where it was known by the startling name of "The Firework." This had not, however, been set up at the time Watt had begun to inquire into the subject. But he found that the college possessed the model of a Newcomen engine for the use of the Natural Philosophy class, which had been sent to London for repair. On hearing of its existence, he suggested to his friend Dr. Anderson, Professor of Natural Philosophy, the propriety of getting back the model; and a sum of money was placed by the Senatus at the professor's disposal, "to recover the steam-engine from Mr. Sisson, instrument-maker in London."

In the mean time Watt sought to learn all that had been written on the subject of the steam-engine. He ascertained from Desaguliers, Switzer, and other writers, what had been accomplished by Savery, Newcomen, Beighton, and others; and he went on with his own independent experiments. His first apparatus was of the simplest possible kind. He used common apothecaries' phials for his steam reservoirs, and canes hollowed out for his steam-pipes. In 1761 he proceeded to experiment on the force of steam by means of a small Papin's digester and a syringe. The syringe was only the third of an inch in diameter, fitted with a solid piston; and it was connected with the digester by a pipe furnished with a stopcock, by which the steam was admitted or shut off at will. It was also itself provided with a stopcock, enabling a communication to be opened between the syringe and the outer air to permit the steam in the syringe to escape. The apparatus, though rude, enabled the experimenter to ascertain some important facts. When the steam in the digester was raised and the cock turned, enabling it to rush against the lower side of the piston, he found that the expansive force of the steam raised a weight of fifteen pounds, with which the piston was loaded. Then on turning on the cock and shutting off the connection with the digester at the same time that a passage was opened to the air, the steam was allowed to escape, when the weight upon the piston, being no longer counteracted, immediately forced it to descend.

Watt saw that it would be easy to contrive that the cocks should be turned by the machinery itself with perfect regularity. But there was an objection to this method. Water is converted into vapor as soon as its elasticity is sufficient to overcome the weight of the air which keeps it down. Under the ordinary pressure of the atmosphere water acquires this necessary elasticity at 212°; but as the steam in the digester was prevented from escaping, it acquired increased heat, and by consequence increased elasticity. Hence it was that the steam which issued from the digester was not only able to support the piston and the air which pressed upon its upper surface, but the additional load with which the piston was weighted. With the imperfect mechanical construction, however, of those days, there was a risk lest the boiler should be burst by the steam, which was apt to force its way through the ill-made joints of the machine. This, conjoined with the great expenditure of steam on the high-pressure system, led Watt to abandon the plan; and the exigencies of his business for a time prevented him from pursuing his experiments.

At length the Newcomen model arrived from London; and in 1763 the little engine, which was destined to become so famous, was put into the hands of Watt. The boiler was somewhat smaller than an ordinary teakettle. The cylinder of the engine was only of two inches diameter and six inches stroke. Watt at first regarded it as merely "a fine plaything." It was, however, enough to set him upon a track of thinking which led to the most important results. When he had repaired the model and set it to work, he found that the boiler, though apparently large enough, could not supply steam in sufficient quantity, and only a few strokes of the piston could be obtained, when the engine stopped. The fire was urged by blowing, and more steam was produced; but still it would not work properly. Exactly at the point at which another man would have abandoned the task in despair, the mind of Watt became thoroughly roused. "Everything," says Professor Robison, "was to him the beginning of a new and serious study; and I knew that he would not quit it till he had either discovered its insignificance or had made something of it." Thus it happened with the phenomena presented by the model of the steam-engine. Watt referred to his books, and endeavored to ascertain from them by what means he might remedy the defects which he found in the model; but they could tell him nothing. He then proceeded with an independent course of experiments, resolved to work out the problem for himself. In the course of his inquiries he came upon a fact which, more than any other, led his mind into the train of thought which at last conducted him to the invention of which the results were destined to prove so stupendous. This fact was the existence of latent heat.

In order to follow the track of investigation pursued by Watt, it is necessary for a moment to revert to the action of the Newcomen pumping-engine. A beam, moving upon a centre, had affixed to one end of it a chain attached to the piston of the pump, and at the other a chain attached to a piston that fitted into the steam-cylinder. It was by driving this latter piston up and down the cylinder that the pump was worked. To communicate the necessary movement to the piston, the steam generated in a boiler was admitted to the bottom of the cylinder, forcing out the air through a valve, where its pressure on the under side of the piston counterbalanced the pressure of the atmosphere on its upper side. The piston, thus placed between two equal forces, was drawn up to the top of the cylinder by the greater weight of the pump-gear at the opposite extremity of the beam. The steam, so far, only discharged the office of the air it displaced; but if the air had been allowed to remain, the piston once at the top of the cylinder could not have returned, being pressed as much by the atmosphere underneath as by the atmosphere above it. The steam, on the contrary, which was admitted by the exclusion of air, could be condensed, and a vacuum created, by injecting cold water through the bottom of the cylinder. The piston, being now unsupported, was forced down by the pressure of the atmosphere on its upper surface. When the piston reached the bottom, the steam was again let in, and the process was repeated. Such was the engine in ordinary use for pumping water at the time that Watt began his investigations.

Among his other experiments, he constructed a boiler which showed by inspection the quantity of water evaporated in any given time, and the quantity of steam used in every stroke of the engine. He was astonished to discover that a small quantity of water in the form of steam heated a large quantity of cold water injected into the cylinder for the purpose of cooling it; and upon further examination he ascertained that steam heated six times its weight of cold water to 212°, which was the temperature of the steam itself. "Being struck with this remarkable fact," says Watt, "and not understanding the reason of it, I mentioned it to my friend Dr. Black, who then explained to me his doctrine of latent heat, which he had taught for some time before this period (the summer of 1764); but having myself been occupied by the pursuits of business, if I had heard of it I had not attended to it, when I thus stumbled upon one of the material facts by which that beautiful theory is supported."