Chapter XII: Section I: James Watt and His Inventions (1)

The success of the Newcomen engine naturally attracted the attention of mechanics, and of scientific men as well, to the possibility of making other applications of steam-power.

The best men of the time gave much attention to the subject, but, until James Watt began the work that has made him famous, nothing more was done than to improve the proportions and slightly alter the details of the Newcomen and Calley engine, even by such skillful engineers as Brindley and Smeaton. Of the personal history of the earlier inventors and improvers of the steam-engine, very little is ascertained; but that of Watt has become well known.

JAMES WATT was of an humble lineage, and was born at Greenock, then a little Scotch fishing village, but now a considerable and a busy town, which annually launches upon the waters of the Clyde a fleet of steamships whose engines are probably, in the aggregate, far more powerful than were all the engines in the world at the date of Watt's birth, January 19, 1736. His grandfather, Thomas Watt, of Crawfordsdyke, near Greenock, was a well-known mathematician about the year 1700, and was for many years a schoolmaster at that place. His father was a prominent citizen of Greenock, and was at various times chief magistrate and treasurer of the town. James Watt was a bright boy, but exceedingly delicate in health, and quite unable to attend school regularly, or to apply himself closely to either study or play. His early education was given by his parents, who were respectable and intelligent people, and the tools borrowed from his father's carpenter-bench served at once to amuse him and to give him a dexterity and familiarity with their use that must undoubtedly have been of inestimable value to him in after-life.

M. Arago, the eminent French philosopher, who wrote one of the earliest and most interesting biographies of Watt, relates anecdotes of him which, if correct, illustrate well his thoughtfulness and his intelligence, as well as the mechanical bent of the boy's mind. He is said, at the age of six years, to have occupied himself during leisure hours with the solution of geometrical problems; and Arago discovers, in a story in which he is described as experimenting with the tea-kettle,[35] his earliest investigations of the nature and properties of steam.

[35] The same story is told of Savery and of Worcester.

When finally sent to the village school, his ill health prevented his making rapid progress; and it was only when thirteen or fourteen years of age that he began to show that he was capable of taking the lead in his class, and to exhibit his ability in the study, particularly, of mathematics. His spare time was principally spent in sketching with his pencil, in carving, and in working at the bench, both in wood and metal. He made many ingenious pieces of mechanism, and some beautiful models. His favorite work seemed to be the repairing of nautical instruments. Among other pieces of apparatus made by the boy was a very fine barrel-organ. In boyhood, as in after-life, he was a diligent reader, and seemed to find something to interest him in every book that came into his hands.

At the age of eighteen, Watt was sent to Glasgow, there to reside with his mother's relatives, and to learn the trade of a mathematical-instrument maker. The mechanic with whom he was placed was soon found too indolent, or was otherwise incapable of giving much aid in the project, and Dr. Dick, of the University of Glasgow, with whom Watt became acquainted, advised him to go to London. Accordingly, he set out in June, 1755, for the metropolis, where, on his arrival, he arranged with Mr. John Morgan, in Cornhill, to work a year at his chosen business, receiving as compensation 20 guineas. At the end of the year he was compelled, by serious ill-health, to return home.

Having become restored to health, he went again to Glasgow in 1756, with the intention of pursuing his calling there. But, not being the son of a burgess, and not having served his apprenticeship in the town, he was forbidden by the guilds, or trades-unions, to open a shop in Glasgow. Dr. Dick came to his aid, and employed him to repair some apparatus which had been bequeathed to the college. He was finally allowed the use of three rooms in the University building, its authorities not being under the municipal rule. He remained here until 1760, when, the trades no longer objecting, he took a shop in the city; and in 1761 moved again, into a shop on the north side of the Trongate, where he earned a scanty living without molestation, and still kept up his connection with the college. He did some work as a civil engineer in the neighborhood of Glasgow, but soon gave up all other employment, and devoted himself entirely to mechanics.

He spent much of his leisure time--of which he had, at first, more than was desirable--in making philosophical experiments and in the manufacture of musical instruments, in making himself familiar with the sciences, and in devising improvements in the construction of organs. In order to pursue his researches more satisfactorily, he studied German and Italian, and read Smith's "Harmonics," that he might become familiar with the principles of construction of musical instruments. His reading was still very desultory; but the introduction of the Newcomen engine in the neighborhood of Glasgow, and the presence of a model in the college collections, which was placed in his hands, in 1763, for repair, led him to study the history of the steam-engine, and to conduct for himself an experimental research into the properties of steam, with a set of improvised apparatus.

Dr. Robison, then a student of the University, who found Watt's shop a pleasant place in which to spend his leisure, and whose tastes affiliated so strongly with those of Watt that they became friends immediately upon making acquaintance, called the attention of the instrument-maker to the steam-engine as early as 1759, and suggested that it might be applied to the propulsion of carriages. Watt was at once interested, and went to work on a little model, having tin steam-cylinders and pistons connected to the driving-wheels by an intermediate system of gearing. The scheme was afterwards given up, and was not revived by Watt for a quarter of a century.

Watt studied chemistry, and was assisted by the advice and instruction of Dr. Black, who was then making the researches which resulted in the discovery of "latent heat." His proposal to repair the model Newcomen engine in the college collections led to his study of Desaguliers's treatise, and of the works of Switzer and others. He thus learned what had been done by Savery and by Newcomen, and by those who had improved the engine of the latter.

In his own experiments he used, at first, apothecaries' phials and hollow canes for steam reservoirs and pipes, and later a Papin's digester and a common syringe. The latter combination made a non-condensing engine, in which he used steam at a pressure of 15 pounds per square inch. The valve was worked by hand, and Watt saw that an automatic valve-gear only was needed to make a working machine. This experiment, however, led to no practical result. He finally took hold of the Newcomen model, which had been obtained from London, where it had been sent for repairs, and, putting it in good working order, commenced experiments with that.

The Newcomen model, as it happened, had a boiler which, although made to a scale from engines in actual use, was quite incapable of furnishing steam enough to work the engine. It was about nine inches in diameter; the steam-cylinder was two inches in diameter, and of six inches stroke of piston, arranged as in Fig. 24, which is a picture of the model as it now appears. It is retained among the most carefully-preserved treasures of the University of Glasgow.

Watt made a new boiler for the experimental investigation on which he was about to enter, and arranged it in such a manner that he could measure the quantity of water evaporated and of steam used at every stroke of the engine.

He soon discovered that it required but a very small quantity of steam to heat a very large quantity of water, and immediately attempted to determine with precision the relative weights of steam and water in the steam-cylinder when condensation took place at the down-stroke of the engine, and thus independently proved the existence of that "latent heat," the discovery of which constitutes, also, one of the greatest of Dr. Black's claims to distinction. Watt at once went to Dr. Black and related the remarkable fact which he had thus detected, and was, in turn, taught by Black the character of the phenomenon as it had been explained to his classes by the latter some little time previously. Watt found that, at the boiling-point, his steam, condensing, was capable of heating six times its weight of water such as was used for producing condensation.

Perceiving that steam, weight for weight even, was a vastly greater absorbent and reservoir of heat than water, Watt saw plainly the importance of taking greater care to economize it than had previously been customary. He first attempted to economize in the boiler, and made boilers with wooden "shells," in order to prevent losses by conduction and radiation, and used a larger number of flues to secure more complete absorption of the heat from the furnace-gases. He also covered his steam-pipes with non-conducting materials, and took every precaution that his ingenuity could devise to secure complete utilization of the heat of combustion. He soon found, however, that he was not working at the most important point, and that the great source of loss was to be found in defects which he noted in the action of the steam in the cylinder. He soon concluded that the sources of loss of heat in the Newcomen engine--which would be greatly exaggerated in a small model--were:

First, the dissipation of heat by the cylinder itself, which was of brass, and was both a good conductor and a good radiator.

Secondly, the loss of heat consequent upon the necessity of cooling down the cylinder at every stroke, in producing the vacuum.

Thirdly, the loss of power due to the pressure of vapor beneath the piston, which was a consequence of the imperfect method of condensation.

He first made a cylinder of non-conducting material--wood soaked in oil and then baked--and obtained a decided advantage in economy of steam. He then conducted a series of very accurate experiments upon the temperature and pressure of steam at such points on the scale as he could readily reach, and, constructing a curve with his results, the abscesses representing temperatures and the pressures being represented by the ordinates, he ran the curve backward until he had obtained closely-approximate measures of temperatures less than 212 deg., and pressures less than atmospheric. He thus found that, with the amount of injection-water used in the Newcomen engine, bringing the temperature of the interior, as he found, down to from 140 deg. to 175 deg. Fahr., a very considerable back-pressure would be met with.

Continuing his examination still further, he measured the amount of steam used at each stroke, and, comparing it with the quantity that would just fill the cylinder, he found that at least _three-fourths was wasted_. The quantity of cold water necessary to produce the condensation of a given weight of steam was next determined; and he found that one pound of steam contained enough heat to raise about six pounds of cold water, as used for condensation, from the temperature of 52 deg. to the boiling-point; and, going still further, he found that he was compelled to use, at each stroke of the Newcomen engine, _four times as much injection-water as should suffice to condense a cylinder full of steam_. This confirmed his previous conclusion that three-fourths of the heat supplied to the engine was wasted.

Watt had now, therefore, determined by his own researches, as he himself enumerates them,[36] the following facts:

[36] Robison's "Mechanical Philosophy," edited by Brewster.

"1. The capacities for heat of iron, copper, and of some sorts of wood, as compared with water.

"2. The bulk of steam compared with that of water.

"3. The quantity of water evaporated in a certain boiler by a pound of coal.

"4. The elasticities of steam at various temperatures greater than that of boiling water, and an approximation to the law which it follows at other temperatures.

"5. How much water in the form of steam was required every stroke by a small Newcomen engine, with a wooden cylinder 6 inches in diameter and 12 inches stroke.

"6. The quantity of cold water required in every stroke to condense the steam in that cylinder, so as to give it a working-power of about 7 pounds on the square inch."

After these well-devised and truly scientific investigations, Watt was enabled to enter upon his work of improving the steam-engine with an intelligent understanding of its existing defects, and with a knowledge of their cause. Watt soon saw that, in order to reduce the losses in the working of the steam in the steam-cylinder, it would be necessary to find some means, as he said, to keep the cylinder "always as hot as the steam that entered it," notwithstanding the great fluctuations of temperature and pressure of the steam during the up and the down strokes. He has told us how, finally, the happy thought occurred to him which relieved him of all difficulty, and led to the series of modifications which at last gave to the world the modern type of steam-engine.

He says:[37] "I had gone to take a walk on a fine Sabbath afternoon. I had entered the Green by the gate at the foot of Charlotte street, and had passed the old washing-house. I was thinking upon the engine at the time, and had gone as far as the herd's house, when the idea came into my mind that, as steam was an elastic body, it would rush into a vacuum, and, if a communication were made between the cylinder and an exhausted vessel, it would rush into it, and might be there condensed without cooling the cylinder. I then saw that I must get rid of the condensed steam and injection-water if I used a jet, as in Newcomen's engine. Two ways of doing this occurred to me: First, the water might be run off by a descending pipe, if an offlet could be got at the depth of 35 or 36 feet, and any air might be extracted by a small pump. The second was, to make the pump large enough to extract both water and air." "I had not walked farther than the Golf-house, when the whole thing was arranged in my mind."

[37] "Reminiscences of James Watt," Robert Hart; "Transactions of
the Glasgow Archaeological Society," 1859.

Referring to this invention, Watt said to Prof. Jardine:[38] "When analyzed, the invention would not appear so great as it seemed to be. In the state in which I found the steam-engine, it was no great effort of mind to observe that the quantity of fuel necessary to make it work would forever prevent its extensive utility. The next step in my progress was equally easy--to inquire what was the cause of the great consumption of fuel. This, too, was readily suggested, viz., the waste of fuel which was necessary to bring the whole cylinder, piston, and adjacent parts from the coldness of water to the heat of steam, no fewer than from 15 to 20 times in a minute." It was by pursuing this train of thought that he was led to devise the separate condenser.

[38] "Lives of Boulton and Watt," Smiles.

On Monday morning Watt proceeded to make an experimental test of his new invention, using for his steam-cylinder and piston a large brass surgeon's-syringe, 1-3/4-inch diameter and 10 inches long. At each end was a pipe leading steam from the boiler, and fitted with a cock to act as a steam-valve. A pipe led also from the top of the cylinder to the condenser, the syringe being inverted and the piston-rod hanging downward for convenience. The condenser was made of two pipes of thin tin plate, 10 or 12 inches long, and about one-sixth of an inch in diameter, standing vertically, and having a connection at the top with a horizontal pipe of larger size, and fitted with a "snifting-valve." Another vertical pipe, about an inch in diameter, was connected to the condenser, and was fitted with a piston, with a view to using it as an "air-pump." The whole was set in a cistern of cold water. The piston-rod of the little steam-cylinder was drilled from end to end to permit the water to be removed from the cylinder. This little model (Fig. 25) worked very satisfactorily, and the perfection of the vacuum was such that the machine lifted a weight of 18 pounds hung upon the piston-rod, as in the sketch. A larger model was immediately afterward constructed, and the result of its test confirmed fully the anticipations which had been awakened by the first experiment.

Having taken this first step and made such a radical improvement, the success of this invention was no sooner determined than others followed in rapid succession, as consequences of the exigencies arising from the first change in the old Newcomen engine. But in the working out of the forms and proportions of the details of the new engine, even Watt's powerful mind, stored as it was with happily-combined scientific and practical information, was occupied for years. In attaching the separate condenser, he first attempted surface-condensation; but this not succeeding well, he substituted the jet. Some provision became at once necessary for preventing the filling of the condenser with water.

Watt at first intended adopting the expedient which had worked satisfactorily with the less effective condensation of Newcomen's engine--i. e., leading a pipe from the condenser to a depth greater than the height of a column of water which could be counterbalanced by the pressure of the atmosphere; but he subsequently employed the air-pump, which relieves the condenser not only of the water, but of the air which also usually collects in considerable volume in the condenser, and vitiates the vacuum. He next substituted oil and tallow for water in the lubrication of the piston and keeping it steam-tight, in order to avoid the cooling of the cylinder incident to the use of the latter. Another cause of refrigeration of the cylinder, and consequent waste of power in its operation, was seen to be the entrance of the atmosphere, which followed the piston down the cylinder at each stroke, cooling its interior by its contact. This the inventor concluded to prevent by covering the top of the cylinder, allowing the piston-rod to play through a "stuffing-box"--which device had long been known to mechanics.

He accordingly not only covered the top, but surrounded the whole cylinder with an external casing, or "steam-jacket," and allowed the steam from the boiler to pass around the steam-cylinder and to press upon the upper surface of the piston, where its pressure was variable at pleasure, and therefore more manageable than that of the atmosphere. It also, besides keeping the cylinder hot, could do comparatively little harm should it leak by the piston, as it could be condensed, and thus readily disposed of.

When he had concluded to build the larger experimental engine, Watt determined to give his whole time and attention to the work, and hired a room in an old deserted pottery near the Broomielaw. Here he worked with a mechanic--John Gardiner, whom he had taken into his employ--uninterruptedly for many weeks. Meantime, through his friend Dr. Black, probably, he had made the acquaintance of Dr. Roebuck, a wealthy physician, who had, with other Scotch capitalists, just founded the celebrated Carron Iron-Works, and had opened a correspondence with him, in which he kept that gentleman informed of the progress of his work on the new engine.

This engine had a steam-cylinder, Watt tells us, of "five or six" inches diameter, and of two feet stroke. It was of copper, smooth-hammered, but not bored out, and "not very true." This was encased in another cylinder of wood. In August, 1765, he tried the small engine, and wrote Dr. Roebuck that he had had "good success," although the machine was very imperfect. "On turning the exhausting-cock, the piston, when not loaded, ascended as quick as the blow of a hammer, and as quick when loaded with 18 pounds (being 7 pounds on the inch) as it would have done if it had had an injection as usual." He then tells his correspondent that he was about to make the larger model. In October, 1765, he finished the latter. The engine, when ready for trial, was still very imperfect. It nevertheless did good work for so rude a machine.

Watt was now reduced to poverty, and, after borrowing considerable sums from friends, he was finally compelled to give up his scheme for the time, and to seek employment in order to provide for his family. During an interval of about two years he supported himself by surveying, and by the work of exploring coal-fields in the neighborhood of Glasgow for the magistrates of the city. He did not, however, entirely give up his invention.

In 1767, Dr. Roebuck assumed Watt's liabilities to the amount of L1,000, and agreed to provide capital for the prosecution of his experiments and to introduce his invention; and, on the other hand, Watt agreed to surrender to Dr. Roebuck two-thirds of the patent. Another engine was next built, having a steam-cylinder seven or eight inches in diameter, which was finished in 1768. This worked sufficiently well to induce the partners to ask for a patent, and the specifications and drawings were completed and presented in 1769.

Watt also built and set up several Newcomen engines, partly, perhaps, to make himself thus thoroughly familiar with the practical details of engine-building. Meantime, also, he prepared the plans for, and finally had built, a moderately large engine of his own new type. Its steam-cylinder was 18 inches in diameter, and the stroke of piston was 5 feet. This engine was built at Kinneil, and was finished in September, 1769. It was not all satisfactory in either its construction or its operation. The condenser was a surface-condenser composed of pipes somewhat like that used in his first little model, and did not prove to be satisfactorily tight. The steam-piston leaked seriously, and repeated trials only served to make more evident its imperfections. He was assisted in this time of need by both Dr. Black and Dr. Roebuck; but he felt strongly the risks which he ran of involving his friends in serious losses, and became very despondent. Writing to Dr. Black, he says: "Of all things in life, there is nothing more foolish than inventing;" and probably the majority of inventors have been led to the same opinion by their own experiences.

"Misfortunes never come singly;" and Watt was borne down by the greatest of all misfortunes--the loss of a faithful and affectionate wife--while still unable to see a successful issue of his schemes. Only less disheartening than this was the loss of fortune of his steadfast friend, Dr. Roebuck, and the consequent loss of his aid. It was at about this time, in the year 1769, that negotiations were commenced which resulted in the transfer of the capitalized interest in Watt's engine to the wealthy manufacturer whose name, coupled with that of Watt, afterward became known throughout the civilized world, as the steam-engine in its new form was pushed into use by his energy and business tact.

Watt met Mr. Boulton, who next became his partner, in 1768, on his journey to London to procure his patent, and the latter had then examined Watt's designs, and, at once perceiving their value, proposed to purchase an interest. Watt was then unable to reply definitely to Boulton's proposition, pending his business arrangements with Dr. Roebuck; but, with Roebuck's consent, afterwards proposed that Boulton should take a one-third interest with himself and partner, paying Roebuck therefor one-half of all expenses previously incurred, and whatever he should choose to add to compensate "for the risk he had run." Subsequently, Dr. Roebuck proposed to transfer to Boulton and to Dr. Small, who was desirous of taking interest with Boulton, one-half of his proprietorship in Watt's inventions, on receiving "a sum not less than one thousand pounds," which should, after the experiments on the engine were completed, be deemed "just and reasonable." Twelve months were allowed for the adjustment of the account. This proposal was accepted in November, 1769.

MATTHEW BOULTON, who now became a partner with James Watt, was the son of a Birmingham silver stamper and piecer, and succeeded to his father's business, building up a great establishment, which, as well as its proprietor, was well known in Watt's time. Watt, writing to Dr. Roebuck before the final arrangement had been made, urged him to close with Boulton for "the following considerations:

"1st. From Mr. Boulton's own character as an ingenious, honest, and rich man. 2dly. From the difficulty and expense there would be of procuring accurate and honest workmen and providing them with proper utensils, and getting a proper overseer or overseers. If, to avoid this inconvenience, you were to contract for the work to be done by a master-workman, you must give up a great share of the profit. 3dly. The success of the engine is far from being verified. If Mr. Boulton takes his chance of success from the account I shall write Dr. Small, and pays you any adequate share of the money laid out, it lessens your risk, and in a greater proportion than I think it will lessen your profits. 4thly. The assistance of Mr. Boulton's and Dr. Small's ingenuity (if the latter engage in it) in improving and perfecting the machine may be very considerable, and may enable us to get the better of the difficulties that might otherwise damn it. Lastly, consider my uncertain health, my irresolute and inactive disposition, my inability to bargain and struggle for my own with mankind: all which disqualify me for any great undertaking. On our side, consider the first outlay and interest, the patent, the present engine, about L200 (though there would not be much loss in making it into a common engine), two years of my time, and the expense of models."

Watt's estimate of the value of Boulton's ingenuity and talent was well-founded. Boulton had shown himself a good scholar, and had acquired considerable knowledge of the languages and of the sciences, particularly of mathematics, after leaving the school from which he graduated into the shop when still a boy. In the shop he soon introduced a number of valuable improvements, and he was always on the lookout for improvements made by others, with a view to their introduction in his business. He was a man of the modern style, and never permitted competitors to excel him in any respect, without the strongest efforts to retain his leading position. He always aimed to earn a reputation for good work, as well as to make money. His father's workshop was at Birmingham; but Boulton, after a time, found that his rapidly-increasing business would compel him to find room for the erection of a more extensive establishment, and he secured land at Soho, two miles distant from Birmingham, and there erected his new manufactory, about 1762.

The business was, at first, the manufacture of ornamental metal-ware, such as metal buttons, buckles, watch-chains, and light filigree and inlaid work. The manufacture of gold and silver plated-ware was soon added, and this branch of business gradually developed into a very extensive manufacture of works of art. Boulton copied fine work wherever he could find it, and often borrowed vases, statuettes, and bronzes of all kinds from the nobility of England, and even from the queen, from which to make copies. The manufacture of inexpensive clocks, such as are now well known throughout the world as an article of American trade, was begun by Boulton. He made some fine astronomical and valuable ornamental clocks, which were better appreciated on the Continent than in England. The business of the Soho manufactory in a few years became so extensive, that its goods were known to every civilized nation, and its growth, under the management of the enterprising, conscientious, and ingenious Boulton, more than kept pace with the accumulation of capital; and the proprietor found himself, by his very prosperity, often driven to the most careful manipulation of his assets, and to making free use of his credit.

Boulton had a remarkable talent for making valuable acquaintances, and for making the most of advantages accruing thereby. In 1758 he made the acquaintance of Benjamin Franklin, who then visited Soho; and in 1766 these distinguished men, who were then unaware of the existence of James Watt, were corresponding, and, in their letters, discussing the applicability of steam-power to various useful purposes. Between the two a new steam-engine was designed, and a model was constructed by Boulton, which was sent to Franklin and exhibited by him in London.

Dr. Darwin seems to have had something to do with this scheme, and the enthusiasm awakened by the promise of success given by this model may have been the origin of the now celebrated prophetic rhymes so often quoted from the works of that eccentric physician and poet. Franklin contributed, as his share in the plan, an idea of so arranging the grate as to prevent the production of smoke. He says: "All that is necessary is to make the smoke of fresh coals pass descending through those that are already ignited." His idea has been, by more recent schemers, repeatedly brought forward as new. Nothing resulted from these experiments of Boulton, Franklin, and Darwin, and the plan of Watt soon superseded all less well-developed plans.

In 1767, Watt visited Soho and carefully inspected Boulton's establishment. He was very favorably impressed by the admirable arrangement of the workshops and the completeness of their outfit, as well as by the perfection of the organization and administration of the business. In the following year he again visited Soho, and this time met Boulton, who had been absent at the previous visit. The two great mechanics were mutually gratified by the meeting, and each at once acquired for the other the greatest respect and esteem. They discussed Watt's plans, and Boulton then definitely decided not to continue his own experiments, although he had actually commenced the construction of a pumping-engine. With Dr. Small, who was also at Soho, Watt discussed the possibility of applying his engine to the propulsion of carriages, and to other purposes. On his return home, Watt continued his desultory labors on his engines, as already described; and the final completion of the arrangement with Boulton, which immediately followed the failure of Dr. Roebuck, took place some time later.

Before Watt could leave Scotland to join his partner at Soho, it was necessary that he should finish the work which he had in hand, including the surveys of the Caledonian canal, and other smaller works, which he had had in progress some months. He reached Birmingham in the spring of 1774, and was at once domiciled at Soho, where he set at work upon the partly-made engines which had been sent from Scotland some time previously. They had laid, unused and exposed to the weather, at Kinneil three years, and were not in as good order as might have been desired. The _block-tin_ steam-cylinder was probably in good condition, but the iron parts were, as Watt said, "perishing," while he had been engaged in his civil engineering work. At leisure moments, during this period, Watt had not entirely neglected his plans for the utilization of steam. He had given much thought, and had expended some time, in experiments upon the plan of using it in a rotary or "wheel" engine. He did not succeed in contriving any plan which seemed to promise success.

It was in November, 1774, that Watt finally announced to his old partner, Dr. Roebuck, the successful trial of the Kinneil engine. He did not write with the usual enthusiasm and extravagance of the inventor, for his frequent disappointments and prolonged suspense had very thoroughly extinguished his vivacity. He simply wrote: "The fire-engine I have invented is now going, and answers much better than any other that has yet been made; and I expect that the invention will be very beneficial to me."

The change of the "atmospheric engine" of Newcomen into the modern steam-engine was now completed in its essential details. The first engine which was erected at Kinneil, near Boroughstoness, had a steam-cylinder 18 inches in diameter. It is seen in the accompanying sketch.

In Fig. 26, the steam passes from the boiler through the pipe _d_ and the valve _c_ to the cylinder-casing or steam-jacket, _Y Y_, and above the piston, _b_, which it follows in its descent in the cylinder, _a_, the valve _f_ being at this time open, to allow the exhaust into the condenser, _h_.

The piston now being at the lower end of the cylinder, and the pump-rods at the opposite end of the beam, _y_, being thus raised and the pumps filled with water, the valves _c_ and _f_ close, while _e_ opens, allowing the steam which remains above the piston to flow beneath it, until, the pressures becoming equal above and below, the weight of the pump-rods overbalancing that of the piston, the latter is rapidly drawn to the top of the cylinder, while the steam is displaced above, passing to the under-side of the piston.

The valve _e_ is next closed, and _c_ and _f_ are again opened; the down-stroke is repeated. The water and air entering the condenser are removed at each stroke by the air-pump, _i_, which communicates with the condenser by the passage _s_. The pump _q_ supplies condensing-water, and the pump _A_ takes away a part of the water of condensation, which is thrown by the air-pump into the "hot-well," _k_, and from it the feed-pump supplies the boiler. The valves are moved by valve-gear very similar to Beighton's and Smeaton's, by the pins, _m m_, in the "plug-frame" or "tappet-rod," _n n_.

The engine is mounted upon a substantial foundation, _B B_. _F_ is an opening out of which, before starting the engine, the air is driven from the cylinder and condenser.

The inventions covered by the patent of 1769 were described as follows:

"My method of lessening the consumption of steam, and consequently fuel, in fire-engines, consists in the following principles:

"1st. That the vessel in which the powers of steam are to be employed to work the engine--which is called 'the cylinder' in common fire-engines, and which I call 'the steam-vessel'--must, during the whole time that the engine is at work, be kept as hot as the steam which enters it; first, by inclosing it in a case of wood, or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor other substances colder than the steam to enter or touch it during that time.

"2dly. In engines that are to be worked, wholly or partially, by condensation of steam, the steam is to be condensed in vessels distinct from the steam-vessel or cylinder, though occasionally communicating with them. These vessels I call condensers; and while the engines are working, these _condensers_ ought at least to be kept as cold as the air in the neighborhood of the engines, by application of water or other cold bodies.

"3dly. Whatever air or other elastic vapor is not condensed by the cold of the condenser, and may impede the working of the engine, is to be drawn out of the steam-vessels or condensers by means of pumps, wrought by the engines themselves, or otherwise.

"4thly. I intend in many cases to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner as the pressure of the atmosphere is now employed in common fire-engines. In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the open air after it has done its office.

"5thly. Where motions round an axis are required, I make the steam-vessels in form of hollow rings or circular channels, with proper inlets and outlets for the steam, mounted on horizontal axles like the wheels of a water-mill. Within them are placed a number of valves that suffer any body to go round the channel in one direction only. In these steam-vessels are placed weights, so fitted to them as to fill up a part or portion of their channels, yet rendered capable of moving freely in them by the means hereinafter mentioned or specified. When the steam is admitted in these engines between these weights and the valves, it acts equally on both, so as to raise the weight on one side of the wheel, and, by the reaction of the valves successively, to give a circular motion to the wheel, the valves opening in the direction in which the weights are pressed, but not in the contrary. As the vessel moves round, it is supplied with steam from the boiler, and that which has performed its office may either be discharged by means of condensers, or into the open air.

"6thly. I intend in some cases to apply a degree of cold not capable of reducing the steam to water, but of contracting it considerably, so that the engines shall be worked by the alternate expansion and contraction of the steam.

"Lastly, instead of using water to render the piston or other parts of the engine air or steam-tight, I employ oils, wax, resinous bodies, fat of animals, quicksilver, and other metals, in their fluid state."

In the construction and erection of his engines, Watt still had great difficulty in finding skillful workmen to make the parts with accuracy, to fit them with care, and to erect them properly when once finished. And the fact that both Newcomen and Watt met with such serious trouble, indicates that, even had the engine been designed earlier, it is quite unlikely that the world would have seen the steam-engine a success until this time, when mechanics were just acquiring the skill requisite for its construction. But, on the other hand, it is not at all improbable that, had the mechanics of an earlier period been as skillful and as well-educated in the manual niceties of their business, the steam-engine might have been much earlier brought into use.

In the time of the Marquis of Worcester it would have probably been found impossible to obtain workmen to construct the steam-engine of Watt, had it been then invented. Indeed, Watt, upon one occasion, congratulated himself that one of his steam-cylinders only lacked _three-eighths_ of an inch of being truly cylindrical.

The history of the steam-engine is from this time a history of the work of the firm of Boulton & Watt. Newcomen engines continued to be built for years after Watt went to Soho, and by many builders. A host of inventors still worked on the most attractive of all mechanical combinations, seeking to effect further improvements. Some inventions were made by contemporaries of Watt, as will be seen hereafter, which were important as being the germs of later growths; but these were nearly all too far in advance of the time, and nearly every successful and important invention which marked the history of steam-power for many years originated in the fertile brain of James Watt.

The defects of the Newcomen engine were so serious, that it was no sooner known that Boulton of Soho had become interested in a new machine for raising water by steam-power, than inquiries came to him from all sides, from mine-owners who were on the point of being drowned out, and from proprietors whose profits were absorbed by the expense of pumping, and who were glad to pay the L5 per horse-power per year finally settled upon as royalty. The London municipal water-works authorities were also ready to negotiate for pumping-engines for raising water to supply the metropolis. The firm was therefore at once driven to make preparations for a large business.

The first and most important matter, however, was to secure an extension of the patent, which was soon to expire. If not renewed, the 15 years of study and toil, of poverty and anxiety, through which Watt had toiled, would prove profitless to the inventor, and the fruits of his genius would have become the unearned property of others. Watt saw, at one time, little hope of securing the necessary act of Parliament, and was greatly tempted to accept a position tendered him by the Russian Government, upon the solicitation of his old friend, Dr. Robison, then a Professor of Mathematics at the Naval School at Cronstadt. The salary was L1,000--a princely income for a man in Watt's circumstances, and a peculiar temptation to the needy mechanic.

Watt, however, went to London, and, with the help of his own and of Boulton's influential friends, succeeded in getting his bill through. His patent was extended 24 years, and Boulton & Watt set about the work of introducing their engines with the industry and enterprise which characterized their every act.

In the new firm, Boulton took charge of the general business, and Watt superintended the design, construction, and erection of their engines. Boulton's business capacity, with Watt's wonderful mechanical ability--Boulton's physical health, and his vigor and courage, offsetting Watt's feeble health and depression of spirits--and, more than all, Boulton's pecuniary resources, both in his own purse and in those of his friends, enabled the firm to conquer all difficulties, whether in finance, in litigation, or in engineering.

It was only after the successful erection and operation of several engines that Boulton and Watt became legally partners. The understood terms were explicitly stated by Watt to include an assignment to Boulton of two-thirds the patent-right; Boulton paying all expenses, advancing stock in trade at an appraised valuation, on which it was to draw interest; Watt making all drawings and designs, and drawing one-third net profits.

As soon as Watt was relieved of the uncertainties regarding his business connections, he married a second wife, who, as Arago says, by "her various talent, soundness of judgment, and strength of character," made a worthy companion to the large-hearted and large-brained engineer. Thenceforward his cares were only such as every business-man expects to be compelled to sustain, and the next ten years were the most prolific in inventions of any period in Watt's life.

From 1775 to 1785 the partners acquired five patents, covering a large number of valuable improvements upon the steam-engine, and several independent inventions. The first of these patents covered the now familiar and universally-used copying-press for letters, and a machine for drying cloth by passing it between copper rollers filled with steam of sufficiently high temperature to rapidly evaporate the moisture. This patent was issued February 14, 1780.

In the following year, October 25, 1781, Watt patented five devices by which he obtained the rotary motion of the engine-shaft without the use of a crank. One of these was the arrangement shown in Fig. 27, and known as the "sun-and-planet" wheels. The crank-shaft carries a gear-wheel, which is engaged by another securely fixed upon the end of the connecting-rod. As the latter is compelled to revolve about the axis of the shaft by a tie which confines the connecting-rod end at a fixed distance from the shaft, the shaft-gear is compelled to revolve, and the shaft with it. Any desired velocity-ratio was secured by giving the two gears the necessary relative diameters. A fly-wheel was used to regulate the motion of the shaft.[39] Boulton & Watt used the sun-and-planet device on many engines, but finally adopted the crank, when the expiration of the patent held by Matthew Wasborough, and which had earlier date than Watt's patent of 1781, permitted them. Watt had proposed the use of a crank, it is said, as early as 1771, but Wasborough anticipated him in securing the patent. Watt had made a model of an engine with a crank and fly-wheel, and he has stated that one of his workmen, who had seen the model, described it to Wasborough, thus enabling the latter to deprive Watt of his own property. The proceeding excited great indignation on the part of Watt; but no legal action was taken by Boulton & Watt, as the overthrow of the patent was thought likely to do them injury by permitting its use by more active competitors and more ingenious men.

[39] For the privilege of using the fly-wheel to regulate the motion
of the engine, Boulton & Watt paid a royalty to Matthew Wasborough,
who had patented it, and who held also the patent for its
combination with a crank, as invented by Pickard and Steed.

The next patent issued to Watt was an exceedingly important one, and of especial interest in a history of the development of the economical application of steam. This patent included:

1. The expansion of steam, and six methods of applying the principle and of equalizing the expansive power.

2. The double-acting steam-engine, in which the steam acts on each side of the piston alternately, the opposite side being in communication with the condenser.

3. The double or coupled steam-engine--two engines capable of working together, or independently, as may be desired.

4. The use of a rack on the piston-rod, working into a sector on the end of the beam, thus securing a perfect rectilinear motion of the rod.

5. A rotary engine, or "steam-wheel."

The efficiency to be secured by the expansion of steam had long been known to Watt, and he had conceived the idea of economizing some of that power, the waste of which was so plainly indicated by the violent rushing of the exhaust-steam into the condenser, as early as 1769. This was described in a letter to Dr. Small, of Birmingham, in May of that year. When experimenting at Kinneil, he had tried to determine the real value of the principle by trial on his small engine.

Boulton had also recognized the importance of this improved method of working steam, and their earlier Soho engines were, as Watt said, made with cylinders "double the size wanted, and cut off the steam at half-stroke." But, though "this was a great saving of steam, so long as the valves remained as at first," the builders were so constantly annoyed by alterations of the valves by proprietors and their engineers, that they finally gave up that method of working, hoping ultimately to be able to resume it when workmen of greater intelligence and reliability could be found. The patent was issued July 17, 1782.

Watt specified a cut-off at one-quarter stroke as usually best.

Watt's explanation of the method of economizing by expansive working, as given to Dr. Small,[40] is worthy of reproduction. He says: "I mentioned to you a method of still doubling the effect of steam, and that tolerably easy, by using the power of steam rushing into a vacuum, at present lost. This would do a little more than double the effect, but it would too much enlarge the vessels to use it all. It is peculiarly applicable to wheel-engines, and may supply the want of a condenser where force of steam is only used; for, open one of the steam-valves and admit steam, until one-fourth of the distance between it and the next valve is filled with steam, shut the valve, and the steam will continue to expand and to pass round the wheel with a diminishing power, ending in one-fourth its first exertion. The sum of this series you will find greater than one-half, though only one-fourth steam was used. The power will indeed be unequal, but this can be remedied by a fly, or in several other ways."

[40] "Lives of Boulton and Watt," Smiles.

It will be noticed that Watt suggests, above, the now well-known non-condensing engine. He had already, as has been seen, described it in his patent of 1769, as also the rotary engine.

Watt illustrates and explains his idea very neatly, by a sketch similar to that here given (Fig. 28).

Steam, entering the cylinder at _a_, is admitted until one-fourth the stroke has been made, when the steam-valve is closed, and the remainder of the stroke is performed without further addition of steam. The variation of steam-pressure is approximately inversely proportional to the variation of its volume. Thus, at half-stroke, the pressure becomes one-half that at which the steam was supplied to the cylinder. At the end of the stroke it has fallen to one-fourth the initial pressure. The pressure is always nearly equal to the product of the initial pressure and volume divided by the volume at the given instant. In symbols,

_PV_
_P'_ = ----.
_V'_

It is true that the condensation of steam doing work changes this law in a marked manner; but the condensation and reevaporation of steam, due to the transfer of heat to and from the metal of the cylinder, tends to compensate the first variation by a reverse change of pressure with change of volume.

The sketch shows this progressive variation of pressure as expansion proceeds. It is seen that the work done per unit of volume of steam as taken from the boiler is much greater than when working without expansion. The product of the mean pressure by the volume of the cylinder is less, but the quotient obtained by dividing this quantity by the volume or weight of steam taken from the boiler, is much greater with than without expansion. For the case assumed and illustrated, the work done during expansion is one and two-fifths times that done previous to cutting off the steam, and the work done per pound of steam is 2.4 times that done without expansion.

Were there no losses to be met with and to be exaggerated by the use of steam expansively, the gain would become very great with moderate expansion, amounting to twice the work done when "following" full stroke, when the steam is cut off at one-seventh. The estimated gain is, however, never realized. Losses by friction, by conduction and radiation of heat, and by condensation and reevaporation in the cylinder--of which losses the latter are most serious--after passing a point which is variable, and which is determined by the special conditions in each case, augment with greater rapidity than the gain by expansion.

In actual practice, it is rarely found, except where special precautions are taken to reduce these losses, that economy follows expansion to a greater number of volumes than about one-half the square root of the steam-pressure; i. e., about twice for 15 or 20 pounds pressure, three times for about 30 pounds, and four and five times for 60 or 65 and for 100 to 125 pounds respectively. Watt very soon learned this general principle; but neither he, nor even many modern engineers, seem to have learned that too great expansion often gives greatly-reduced economy.

The inequality of pressure due to expansion, to which he refers, was a source of much perplexity to Watt, as he was for a long time convinced that he must find some method of "equalizing" the consequent irregular effort of the steam upon the piston. The several methods of "equalizing the expansive power" which are referred to in the patent were attempts to secure this result. By one method, he shifted the centre as the beam vibrated, thus changing the lengths of the arms of that great lever, to compensate the change of moment consequent upon the change of pressure. He finally concluded that a fly-wheel, as first proposed by Fitzgerald, who advised its use on Papin's engine, would be the best device on engines driving a crank, and trusted to the inertia of a balance-weight in his pumping-engines, or to the weight of the pump-rods, and permitted the piston to take its own speed so far as it was not thus controlled.

The double-acting engine was a modification of the single-acting engine, and was very soon determined upon after the successful working of the latter had become assured.