Part 11

After having satisfied my curiosity about Jack the Darter, I proceeded to Birmingham. I mentioned that I travelled in a carriage of a singular construction. It was a one-wheeled chaise, which I had had made for the purpose of going conveniently in narrow roads. It was made fast by shafts to the horse's sides, and was furnished with two weights or counterpoises, that hung below the shafts. The seat was not more than eight and twenty or thirty inches from the ground, in order to bring the centre of gravity of the whole as low as possible. The footboard turned upon hinges fastened to the shafts, so that when it met with any obstacle it gave way, and my legs were warned to lift themselves up. In going through water my legs were secured by leathers, which folded up like the sides of bellows; by this means I was pretty safe from wet. On my road to Birmingham I passed through Long Compton, in Warwickshire, on a Sunday. The people were returning from church, and numbers stopped to gaze at me. There is, or was, a shallow ford near the town, over which there was a very narrow bridge for horse and foot passengers, but not sufficiently wide for wagons or chaises. Towards this bridge I drove. The people, not perceiving the structure of my one-wheeled vehicle, called to me with great eagerness to warn me that the bridge was too narrow for carriages. I had an excellent horse, which went so fast as to give but little time for examination. The louder they called, the faster I drove; and when I had passed the bridge, they shouted after me with surprise. I got on to Shipstone upon Stone; but before I had dined there I found that my fame had overtaken me. My carriage was put into a coach-house, so that those who came from Long Compton, not seeing it, did not recognize me. I therefore had an opportunity of hearing all the exaggerations and strange conjectures which were made by those who related my passage over the narrow bridge. There were posts on the bridge, to prevent, as I suppose, more than one horseman from passing at once. Some of the spectators asserted that my carriage had gone over these posts; others said that it had not wheels, which was indeed literally true; but they meant to say that it was without any wheel. Some were sure that no carriage ever went so fast; and all agreed that at the end of the bridge, where the floods had laid the road for some way under water, my carriage swam on the surface of the water.

VIII.

JAMES WATT.

"Uncle Fritz," said Mabel Liddell, the next afternoon that our friends had gathered together for a reading, "would it not be well for us all to go down into the kitchen this afternoon, and watch the steam come out of the kettle as Ellen makes tea for us?"

"Why should it be well, Mabel?" said Colonel Ingham. "For my part, I should prefer to remain in my own room, more especially as I consider my armchair to be more suited to the comfort of one already on the downward path in life than is the kitchen table, where we should have to sit should we invade the premises of our friends below."

"I was thinking," said Mabel, "of the manner in which James Watt when a child invented the steam-engine, from observing the motion of the top of the teakettle; and as we are to read about Watt this afternoon I thought we might be in a more fit condition to understand his invention, and might more fully comprehend his frame of mind while perfecting his great work, should we also fix our eyes and minds on the top of the teakettle in Ellen's kitchen."

"Mabel, my child," said Uncle Fritz, "you talk like a book, and a very interesting one at that; but I think, as the youngest of us would say, that you are just a little off in your remarks. And as I observe that Clem, who is going to read this afternoon, desires to deliver a sermon of which your conversation seems to be the text, I will request all to listen to him before we consider seriously vacating this apartment, however poor it may be,"--and he glanced fondly around at the comfortable arrangements that everywhere pervaded the study,--"and seek the regions below."

"I only wanted to say," began Clem, "that although Watt did on one occasion (in his extreme youth) look at a teakettle with some interest, he was not in the habit, at the time when he devoted most thought to the steam-engine, of having a teakettle continually before him that he might gain inspiration from observing the steam issue from its nose. And, as Watt dispensed with this aid, I have no doubt that we may do so as well, contenting ourselves with the results of the experiments in the vaporization of water, which Ellen is now conducting in the form of tea. Besides all this, however, I do want to say some things, before we read aloud this afternoon (I hope this isn't really too much like a sermon), about the steam-engine and the part that Watt had in perfecting it."

At this point the irrepressible Mabel was heard to whisper to Bedford, who sat next her: "Wasn't it curious that the same mind which grasped the immense capabilities of the steam-engine should have been able also to construct such a delicate lyric as

'How doth the little busy bee Improve each shining hour'?"

"Mabel," said Colonel Ingham, "you are absolutely unbearable. If you do not keep in better order I shall be sorry that I dissuaded you from descending to the kitchen. I see nothing incongruous myself in indulging in mechanical experiments, and in throwing one's thoughts into the form of verse,"--here the old gentleman colored slightly, as though he recollected something of the sort,--"but it may be well to counteract the impression your conversation may have made by stating that Isaac Watts did not invent the steam-engine, nor did James Watt write the beautiful words you have just quoted.--Now, Clem, I believe you have the floor."

"Well," said Clem, "I only want the floor for a short time in order to explain about Watt and the steam-engine, and how much he was the inventor of it, before we begin to read.

"There are various points about the steam-engine which are really Watt's invention,--the separate condenser, for instance,--but the idea of the steam-engine was not original with him; that is, when he saw the steam in the teakettle raise the lid and drop it again, he was not the first to speculate on the power of steam."

"Are you going to read us that part in the book, Clem?" asked Bedford, with some interest.

"Yes, if you like," said Clem. "I guess it tells about it in Mr. Smiles's 'Life of Watt.'" So he began to overhaul the book he had brought, and shortly discovered the anecdote referred to by Mabel with such interest, and read it.

"On one occasion he [James Watt] was reproved by Mrs. Muirhead, his aunt, for his indolence at the tea-table. 'James Watt,' said the worthy lady, 'I never saw such an idle boy as you are. Take a book, or employ yourself usefully; for the last hour you have not spoken one word, but taken off the lid of that kettle and put it on again, holding now a cup and now a silver spoon over the steam, watching how it rises from the spout, catching and counting the drops it falls into.' In the view of M. Arago, the little James before the teakettle, becomes the great engineer, preparing the discoveries which were soon to immortalize him. In our opinion, the judgment of the aunt was the truest. There is no reason to suppose that the mind of the boy was occupied with philosophical theories on the condensation of steam, which he compassed with so much difficulty in his maturer years. This is more probably an afterthought borrowed from his subsequent discoveries. Nothing is commoner than for children to be amused with such phenomena in the same way that they will form air-bubbles in a cup of tea, and watch them sailing over the surface till they burst. The probability is that little James was quite as idle as he seemed."

"That is very interesting," remarked Mabel. "Don't you think now, Uncle Fritz, we had better go into the kitchen?" And she looked appealingly at the old gentleman, who merely held up his finger for silence as Clem continued his lecture.

"What I meant to say," Clem went on, "was that other people before Watt had found out the power of steam, and had used it too. There was one Hero of Alexandria, who lived about two thousand years ago, who used steam for many interesting purposes, notably for animating various figures that took part in the idolatrous worship of his time, and thus in deceiving the common people. But his contrivances, though engines which went by steam, would hardly be called steam-engines. Between Hero of Alexandria, of 160 B. C., and the Marquis of Worcester, of 1650 A. D., there does not seem to have been much doing in the way of inventing the steam-engine. But the Marquis of Worcester in Charles II.'s time was a great philosopher, and did nobody knows exactly what with steam. But though he did great things, he did not produce a particularly capable engine, though he seems to have known more about steam than anybody else did at his time. After the Marquis of Worcester and before Watt, there were three men who did much towards inventing and improving the steam-engine. Their names were Savery, Papin, and Newcomen. I don't propose to tell you about the inventions of each one; but it's well enough to remember that each one did important service in getting the steam-engine to the point where Watt took hold of it. As it was on Newcomen's engine that Watt made his first serious experiments, I think we should all like to know something about it."

THE NEWCOMEN ENGINE.

Newcomen's engine may be thus briefly described: The steam was generated in a separate boiler, as in Savery's engine, from which it was conveyed into a vertical cylinder underneath a piston fitting it closely, but movable upwards and downwards through its whole length. The piston was fixed to a rod, which was attached by a joint or chain to the end of a lever vibrating upon an axis, the other end being attached to a rod working a pump. When the piston in the cylinder was raised, steam was let into the vacated space through a tube fitted into the top of the boiler, and mounted with a stopcock. The pump-rod at the further end of the lever being thus depressed, cold water was applied to the sides of the cylinder, on which the steam within it was condensed, a vacuum was produced, and the external air, pressing upon the top of the piston, forced it down into the empty cylinder. The pump-rod was thereby raised; and, the operation of depressing it being repeated, a power was thus produced which kept the pump continuously at work. Such, in a few words, was the construction and action of Newcomen's first engine.[8]

While the engine was still in its trial state, a curious accident occurred which led to a change in the mode of condensation, and proved of essential importance in establishing Newcomen's engine as a practical 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 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 continued 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 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_ (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.