Chapter XIII: Section I: James Watt and His Inventions (2)

Watt had covered in the top of his single-acting engine, to prevent cooling the interior of the cylinder by contact with the comparatively cold atmosphere. When this had been done, there was but a single step required to convert the machine into the double-acting engine. This alteration, by which the steam was permitted to act upon the upper and the lower sides of the piston alternately, had been proposed by Watt as early as 1767, and a drawing of the engine was laid before a committee of the House of Commons in 1774-'75. By this simple change Watt doubled the power of his engine. Although invented much earlier, the plan was not patented until he was, as he states, driven to take out the patent by the "plagiarists and pirates" who were always ready to profit by his ingenuity. This form of engine is now almost universally used. The single-acting pumping-engine remains in use in Cornwall, and in a few other localities, and now and then an engine is built for other purposes, in which steam acts only on one side of the piston; but these are rare exceptions to the general rule.

The subject of his next invention was not less interesting. The double-cylinder or "compound" engine has now, after the lapse of nearly a century, become an important and usual type of engine. It is impossible to determine precisely to whom to award the credit of its first conception. Dr. Falk, in 1779, had proposed a double-acting engine, in which there were two single-acting cylinders, acting in opposite directions and alternately on opposite sides of a wheel, with which a rack on the piston-rod of each geared.

Watt claimed that Hornblower, the patentee of the "compound engine," was an infringer upon his patents; and, holding the patent on the separate condenser, he was able to prevent the engine of his competitor taking such form as to be successfully introduced. The Hornblower engine was soon given up.

Watt stated that this form of engine had been invented by him as early as 1767, and that he had explained its peculiarities to Smeaton and others several years before Hornblower attempted to use it. He wrote to Boulton: "It is no less than our double-cylinder engine, worked upon our principle of expansion." He never made use of the plan, however; and the principal object sought, apparently, in patenting this, as well as many other devices, was to secure himself against competition.

The rack and sector patented at this time was soon superseded by the parallel-motion; and the last claim, the "steam-wheel" or rotary engine, although one was built of considerable size, was not introduced.

After the patent of 1782 had been secured, Watt turned his attention, when not too hard-pressed by business, to other schemes, and to experimenting with still other modifications and applications of his engine. He had, as early as 1777, proposed to make a steam-hammer for Wilkinson's forge; but he was too closely engaged with more important matters to take hold of the project with much earnestness until late in the year 1782, when, after some preliminary trials, he reported, December 13th: "We have tried our little tilting-forge hammer at Soho with success. The following are some of the particulars: Cylinder, 15 inches in diameter; 4 feet stroke; strokes per minute, 20. The hammer-head, 120 pounds weight, rises 8 inches, and strikes 240 blows per minute. The machine goes quite regularly, and can be managed as easily as a water-mill. It requires a very small quantity of steam--not above half the contents of the cylinder per stroke. The power employed is not more than one-fourth of what would be required to raise the quantity of water which would enable a water-wheel to work the same hammer with the same velocity."

He immediately set about making a much heavier hammer, and on April 26, 1783, he wrote that he had done "a thing never done before"--making his hammer strike 300 blows a minute. This hammer weighed 7-1/2 hundredweight, and had a drop of 2 feet. The steam-cylinder had a diameter of 42 inches and 6 feet stroke of piston, and was calculated to have sufficient power to drive four hammers weighing 7 hundredweight each. The engine made 20 strokes per minute, the hammer giving 90 blows in the same time.

This new application of steam-power proving successful, Watt next began to develop a series of minor inventions, which were finally secured by his patent of April 27, 1784, together with the steam tilt-hammer, and a steam-carriage, or "locomotive engine."

The contrivance previously used for guiding the head of the piston-rod--the sectors and chains, or rack--had never given satisfaction. The rudeness of design of the contrivance was only equalled by its insecurity. Watt therefore contrived a number of methods of accomplishing the purpose, the most beautiful and widely-known of which is the "parallel-motion," although it has now been generally superseded by one of the other devices patented at the same time--the cross-head and guides. As originally proposed, a rod was attached to the head of the piston-rod, standing vertically when the latter was at quarter-stroke. The upper end of this rod was pivoted to the end of the beam, and the lower end to the extremity of a horizontal rod having a length equal to one-half the length of the beam. The other end of the horizontal rod was coupled to the frame of the engine. As the piston rose and fell, the upper and lower ends of the vertical rod were swayed in opposite directions, and to an equal extent, by the beam and the lower horizontal rod, the middle point at which the piston-rod was attached preserving its position in the vertical line. This form was objectionable, as the whole effort of the engine was transmitted through the parallel-motion rods. Another form is shown in the sketch given of the double-acting engine in Fig. 31, which was free from this defect. The head of the piston-rod, _g_, was guided by rods connecting it with the frame at _c_, and forming a "parallelogram," _g d e b_, with the beam. Many varieties of "parallel-motion" have been devised since Watt's invention was attached to his engines at Soho. They usually are more or less imperfect, guiding the piston-rod in a line only approximately straight.

The cross-head and guides are now generally used, very much as described by Watt in this patent as his "second principle." This device will be seen in the engravings given hereafter of more modern engines. The head of the piston-rod is fitted into a transverse bar, or cross-head, which carries properly-shaped pieces at its extremities, to which are bolted "gibs," so made as to fit upon guides secured to the engine-frame. These guides are adjusted to precise parallelism with the centre line of the cylinder. The cross-head, sliding in or on these guides, moves in a perfectly straight line, and, compelling the piston-rod to move with it, the latter is even more perfectly guided than by a parallel-motion. This arrangement, where properly proportioned, is not necessarily subject to great friction, and is much more easily adjusted and kept in line than the parallel-motion when wear occurs or maladjustment takes place.

By the same patent, Watt secured the now common "puppet-valve" with beveled seat, and the application of the steam-engine to driving rolling-mills and hammers for forges, and to "wheel-carriages for removing persons or goods, or other matters, from place to place." For the latter purpose he proposes to use boilers "of wood, or of thin metal, strongly secured by hoops or otherwise," and containing "internal fire-boxes." He proposed to use a condenser cooled by currents of air.

It would require too much space to follow Watt in all his schemes for the improvement and for the application of the steam-engine. A few of the more important and more ingenious only can be described. Many of the contracts of Boulton & Watt gave them, as compensation for their engines, a fraction--usually one-third--of the value of the fuel saved by the use of the Watt engine in place of the engine of Newcomen, the amount due being paid annually or semiannually, with an option of redemption on the part of the purchaser at ten years' purchase. This form of agreement compelled a careful determination, often, of the work done and fuel consumed by both the engine taken out and that put in its place. It was impossible to rely upon any determination by personal observation of the number of strokes made by the engine. Watt therefore made a "counter," like that now familiar to every one as used on gas-meters. It consists of a train of wheels moving pointers on several dials, the first dial showing tens, the second hundreds, the third thousands, etc., strokes or revolutions. Motion was communicated to the train by means of a pendulum, the whole being mounted on the beam of the engine, where every vibration produced a swing of the pendulum. Eight dials were sometimes used, the counter being set and locked, and only opened once a year, when the time arrived for determining the work done during the preceding twelve-month.

The application of his engine to purposes for which careful adjustment of speed was requisite, or where the load was subject to considerable variation, led to the use of a controlling-valve in the steam-pipe, called the "throttle-valve," which was adjustable by hand, and permitted the supply of steam to the engine to be adjusted at any instant and altered to any desired extent. It is now given many forms, but it still is most usually made just as originally designed by Watt. It consists of a circular disk, which just closes up the steam-pipe when set directly across it, or of an elliptical disk, which closes the pipe when standing at an angle of somewhat less than 90 deg. with the line of the pipe. This disk is carried on a spindle extending through the pipe at one side, and carrying on its outer end an arm by means of which it may be turned into any position. When placed with its face in line with the pipe, it offers very little resistance to the flow of steam to the engine. When set in the other position, it shuts off steam entirely and stops the engine. It is placed in such position at any time, that the speed of the engine is just that required at the time. In the engraving of the double-acting engine with fly-wheel (Fig. 31), it is shown at _T_, as controlled by the governor.

The governor, or "fly-ball governor," as it is often distinctively called, was another of Watt's minor but very essential inventions. Two heavy iron or brass balls, _B B'_, were suspended from pins, _C C'_, in a little cross-piece carried on the head of a vertical spindle, _A A'_, driven by the engine. The speed of the engine varying, that of the spindle changed correspondingly, and the faster the balls were swung the farther they separated. When the engine's speed decreased, the period of revolution of the balls was increased, and they fell back toward the spindle. Whenever the velocity of the engine was uniform, the balls preserved their distance from the spindle and remained at the same height, their altitude being determined by the relation existing between the force of gravity and centrifugal force in the temporary position of equilibrium. The distance from the point of suspension down to the level of the balls is always equal to 9.78 inches divided by the square of the number of revolutions per second--i. e., _h_ = 9.78 (1/_N_^2) = 0.248 (1/_N_^2) meters.

The arms carrying the balls, or the balls themselves, are pinned to rods, _M M'_, which are connected to a piece, _N N'_, sliding loosely on the spindle. A score, _T_, cut in this piece engages a lever, _V_, and, as the balls rise and fall, a rod, _W_, is moved, closing and opening the throttle-valve, and thus adjusting the supply of steam in such a way as to preserve a nearly fixed speed of engine. The connection with the throttle-valve and with the cut-off valve-gear is seen not only in the engraving of the double-acting Watt engine, but also in those of the Greene and the Corliss engines. This contrivance had previously been used in regulating water-wheels and windmills. Watt's invention consisted in its application to the regulation of the steam-engine.

Still another useful invention of Watt's was his "mercury steam-gauge"--a barometer in which the height of the mercury was determined by the pressure of the steam instead of that of the atmosphere. This simple instrument consisted merely of a bent tube containing a portion of mercury. One leg, _B D_, of this U-tube was connected with the steam-pipe, or with the boiler by a small steam-pipe; the other end, _C_, was open to the atmosphere. The pressure of the steam on the mercury in _B D_ caused it to rise in the other "leg" to a height exactly proportioned to the pressure, and causing very nearly two inches difference of level to the pound, or one inch to the pound actual rise in the outer leg. The rude sketch from Farey, here given (Fig. 30), indicates sufficiently well the form of this gauge. It is still considered by engineers the most reliable of all forms of steam-gauge. Unfortunately, it is not conveniently applicable at high pressure. The scale, _A_, is marked with numbers indicating the pressure, which numbers are indicated by the head of a rod floating up with the mercury.

A similar gauge was used to determine the degree of perfection of vacuum attained in the condenser, the mercury falling in the outer leg as the vacuum became more complete. A perfect vacuum would cause a depression of level in that leg to 30 inches below the level of the mercury in the leg connected with the condenser. In a more usual form, it consisted of a simple glass tube having its lower end immersed in a cistern of mercury, as in the ordinary barometer, the top of the tube being connected with a pipe leading to the condenser. With a perfect vacuum in the condenser, the mercury would rise in the tube very nearly 30 inches. Ordinarily, the vacuum is not nearly perfect, and, a back pressure remaining in the condenser of one or two pounds per square inch, the atmospheric pressure remaining unbalanced is only sufficient to raise the mercury 26 or 28 inches above the level of the liquid metal in the cistern.

To determine the height of water in his boiler, Watt added to the gauge-cocks already long in use the "glass water-gauge," which is still seen in nearly every well-arranged boiler. This was a glass tube, _a a'_ (Fig. 30), mounted on a standard attached to the front of the boiler, and at such a height that its middle point was very little below the proposed water-level. It was connected by a small pipe, _r_, at the top to the steam-space, and another little pipe, _r'_, led into the boiler from its lower end below the water-line. As the water rose and fell within the boiler, its level changed correspondingly in the glass. This little instrument is especially liked, because the position of the water is at all times shown to the eye of the attendant. If carefully protected against sudden changes of temperature, it answers perfectly well with even very high pressures.

The engines built by Boulton & Watt were finally fitted with the crank and fly-wheel for application to the driving of mills and machinery. The accompanying engraving (Fig. 31) shows the engine as thus made, combining all of the essential improvements designed by its inventor.

In the engraving, _C_ is the steam-cylinder, _P_ the piston, connected to the beam by the link, _g_, and guided by the parallel-motion, _g d c_. At the opposite end of the beam a connecting-rod, _O_, connects with the crank and fly-wheel shaft. _R_ is the rod of the air-pump, by means of which the condenser is kept from being flooded by the water used for condensation, which water-supply is regulated by an "injection-handle," _E_. A pump-rod, _N_, leads down from the beam to the cold-water pump, by which water is raised from the well or other source to supply the needed injection-water. The air-pump rod also serves as a "plug-rod," to work the valves, the pins at _m_ and _R_ striking the lever, _m_, at either end of the stroke. When the piston reaches the top of the cylinder, the lever, _m_, is raised, opening the steam-valve, _B_, at the top, and the exhaust-valve, _E_, at the bottom, and at the same time closing the exhaust at the top and the steam at the bottom. When the entrance of steam at the top and the removal of steam-pressure below the piston has driven the piston to the bottom, the pin, _R_, strikes the lever, _m_, opening the steam and closing the exhaust valve at the bottom, and similarly reversing the position of the valves at the top. The position of the valves is changed in this manner with every reversal of the motion of the piston as the crank "turns over the centre."

The earliest engines of the double-acting kind, and of any considerable size, which were built to turn a shaft, were those which were set up in the Albion Mills, near Blackfriars' Bridge, London, in 1786, and destroyed when the mills burned down in 1791. There were a pair of these engines (shown in Fig. 27), of 50 horse-power each, and geared to drive 20 pairs of stones, making fine flour and meal. Previous to the erection of this mill the power in all such establishments had been derived from windmills and water-wheels. This mill was erected by Boulton & Watt, and capitalists working with them, not only to secure the profit anticipated from locating a flour-mill in the city of London, but also with a view to exhibiting the capacity of the new double-acting "rotating" engine. The plan was proposed in 1783, and work was commenced in 1784; but the mill was not set in operation until the spring of 1786. The capacity of the mill was, in ordinary work, 16,000 bushels of wheat ground into fine flour per week. On one occasion, the mill turned out 3,000 bushels in 24 hours. In the construction of the machinery of the mill, many improvements upon the then standard practice were introduced, including cast-iron gearing with carefully-formed teeth and iron framing. It was here that John Rennie commenced his work, after passing through his apprenticeship in Scotland, sending his chief assistant, Ewart, to superintend the erection of the milling machinery. The mill was a success as a piece of engineering, but a serious loss was incurred by the capitalists engaged in the enterprise, as it was set on fire a few years afterward and entirely destroyed. Boulton and Watt were the principal losers, the former losing L6,000, and the latter L3,000.

The valve-gear of this engine, a view of which is given in Fig. 27, was quite similar to that used on the Watt pumping-engine. The accompanying illustration (Fig. 32) represents this valve-motion as attached to the Albion Mills engine.

The steam-pipe, _a b d d e_, leads the steam from the boiler to the chambers, _b_ and _e_. The exhaust-pipe, _g g_, leads from _h_ and _i_ to the condenser. In the sketch, the upper steam and the lower exhaust valves, _b_ and _f_, are opened, and the steam-valve, _e_, and exhaust-valve, _c_, are closed, the piston being near the upper end of the cylinder and descending. _l_ represents the plug-frame, which carries tappets, 2 and 3, which engage the lever, _s_, at either end of its throw, and turn the shaft, _u_, thus opening and closing _c_ and _e_ simultaneously by means of the connecting-links, 13 and 14. A similar pair of tappets on the opposite side of the plug-rod move the valves, _b_ and _f_, by means of the rods, 10 and 11, the arm, _r_, when struck by those tappets, turning the shaft, _t_, and thus moving the arms to which those rods are attached. Counterbalance-weights, carried on the ends of the arms, 4 and 15, retain the valves on their seats when closed by the action of the tappets. When the piston nearly reaches the lower end of the cylinder, the tappet, 1, engages the arm, _r_, closing the steam-valve, _b_, and the next instant shutting the exhaust-valve, _f_. At the same time, the tappet, 3, by moving the arm, _s_, downward, opens the steam-valve, _e_, and the exhaust-valve, _c_. Steam now no longer issues from the steam-pipe into the space, _c_, and thence into the engine-cylinder (not shown in the sketch); but it now enters the engine through the valve, _e_, forcing the piston upwards. The exhaust is simultaneously made to occur at the upper end, the rejected steam passing from the engine into the space, _c_, and thence through _c_ and the pipe, _g_, into the condenser.

This kind of valve-gear was subsequently greatly improved by Murdoch, Watt's ingenious and efficient foreman, but it is now entirely superseded on engines of this class by the eccentric, and the various forms of valve-gear driven by it.

The "trunk-engine" was still another of the almost innumerable inventions of Watt. A half-trunk engine is described in his patent of 1784, as shown in the accompanying sketch (Fig. 33), in which _A_ is the cylinder, _B_ the piston, and _C_ its rod, encased in the half-trunk, _D_. The plug-rod, _G_, moves the single pair of valves by striking the catches, _E_ and _F_, as was usual with Watt's earlier engines.

Watt's steam-hammer was patented at the same time. It is seen in Fig. 34, in which _A_ is the steam-cylinder and _B_ its rod, the engine being evidently of the form just described. It works a beam, _C C_, which in turn, by the rod, _M_, works the hammer-helve, _L J_, and the hammer, _L_. The beam, _F G_, is a spring, and the block, _N_, the anvil.

Watt found it impossible to determine the duty of his engines at all times by measurement of the work itself, and endeavored to find a way of ascertaining the power produced, by ascertaining the pressure of steam within the cylinder. This pressure was so variable, and subject to such rapid as well as extreme fluctuations, that he found it impossible to make use of the steam-gauge constructed for use on the boiler. He was thus driven to invent a special instrument for this work, which he called the "steam-engine indicator." This consisted of a little steam-cylinder containing a nicely-fitting piston, which moved without noticeable friction through a range which was limited by the compression of a helical spring, by means of which the piston was secured to the top of its cylinder. The distance through which the piston rose was proportional to the pressure exerted upon it, and a pointer attached to its rod traversed a scale upon which the pressure per square inch could be read. The lower end of the instrument being connected with the steam-cylinder of the engine by a small pipe fitted with a cock, the opening of the latter permitted steam from the engine-cylinder to fill the indicator-cylinder, and the pressure of steam was always the same in both cylinders. The indicator-pointer therefore traversed the pressure-scale, always exhibiting the pressure existing at the instant in the cylinder of the engine. When the engine was at rest and steam off, the indicator-piston stood at the same level as when detached from the engine, and the pointer stood at 0 on the scale. When steam entered, the piston rose and fell with the fluctuations of pressure; and when the exhaust-valve opened, discharging the steam and producing a vacuum in the steam-cylinder, the pointer of the indicator dropped below 0, showing the degree of exhaustion. Mr. Southern, one of Watt's assistants, fitted the instrument with a sliding board, moved horizontally backward and forward by a cord or link-work connecting directly or indirectly with the engine-beam, and thus giving it a motion coincident with that of the piston. This board carried a piece of paper, upon which a pencil attached to the indicator piston-rod drew a curve. The vertical height of any point on this curve above the base-line measured the pressure in the cylinder at the moment when it was made, and the horizontal distance of the point from either end of the diagram determined the position, at the same moment, of the engine-piston. The curve thus inscribed, called the "indicator card," or indicator diagram, exhibiting every minute change in the pressure of steam in the engine, not only enabled the mean pressure and the power of the engine to be determined by its measurement, but, to the eye of the expert engineer, it was a perfectly legible statement of the position of the valves of the engine, and revealed almost every defect in the action of the engine which could not readily be detected by external examination. It has justly been called the "engineers' stethoscope," opening the otherwise inaccessible parts of the steam-engine to the inspection of the engineer even more satisfactorily than the stethoscope of the physician gives him a knowledge of the condition and working of organs contained within the human body. This indispensable and now familiar engineers' instrument has since been modified and greatly improved in detail.

The Watt engine had, by the construction of the improvements described in the patents of 1782-'85, been given its distinctive form, and the great inventor subsequently did little more than improve it by altering the forms and proportions of its details. As thus practically completed, it embodied nearly all the essential features of the modern engine; and, as we have seen, the marked features of our latest practice--the use of the double cylinder for expansion, the cut-off valve-gear, and surface-condensation--had all been proposed, and to a limited extent introduced. The growth of the steam-engine has here ceased to be rapid, and the changes which followed the completion of the work of James Watt have been minor improvements, and rarely, if ever, real developments.

Watt's mind lost none of its activity, however, for many years. He devised and patented a "smoke-consuming furnace," in which he led the gases produced on the introduction of fresh fuel over the already incandescent coal, and thus burned them completely. He used two fires, which were coaled alternately. Even when busiest, also, he found time to pursue more purely scientific studies. With Boulton, he induced a number of well-known scientific men living near Birmingham to join in the formation of a "Lunar Society," to meet monthly at the houses of its members, "at the full of the moon." The time was thus fixed in order that those members who came from a distance should be able to drive home, after the meetings, by moonlight. Many such societies were then in existence in England; but that at Birmingham was one of the largest and most distinguished of them all. Boulton, Watt, Drs. Small, Darwin, and Priestley, were the leaders, and among their occasional visitors were Herschel, Smeaton, and Banks. Watt called these meetings "Philosophers' meetings." It was during the period of most active discussion at the "philosophers' meetings" that Cavendish and Priestley were experimenting with mixtures of oxygen and hydrogen, to determine the nature of their combustion. Watt took much interest in the subject, and, when informed by Priestley that he and Cavendish had both noticed a deposit of moisture invariably succeeding the explosion of the mixed gases, when contained in a cold vessel, and that the weight of this water was approximately equal to the weight of the mixed gases, he at once came to the conclusion that the union of hydrogen with oxygen produced water, the latter being a chemical compound, of which the former were constituents. He communicated this reasoning, and the conclusions to which it had led him, to Boulton, in a letter written in December, 1782, and addressed a letter some time afterward to Priestley, which was to have been read before the Royal Society in April, 1783. The letter was not read, however, until a year later, and, three months after, a paper by Cavendish, making the same announcement, had been laid before the Society. Watt stated that both Cavendish and Lavoisier, to whom also the discovery is ascribed, received the idea from him.

The action of chlorine in bleaching organic coloring-matters, by (as since shown) decomposing them and combining with their hydrogen, was made known to Watt by M. Berthollet, the distinguished French chemist, and the former immediately introduced its use into Great Britain, by inducing his father-in-law, Mr. Macgregor, to make a trial of it.

The copartnership of Boulton & Watt terminated by limitation, and with the expiration of the patents under which they had been working, in the first year of the present century; and both partners, now old and feeble, withdrew from active business, leaving their sons to renew the agreement and to carry on the business under the same firm-style.

Boulton, however, still interested himself in some branches of manufacture, especially in his mint, where he had coined many years and for several nations.

Watt retired, a little later, to Heathfield, where he passed the remainder of his life in peaceful enjoyment of the society of his friends, in studies of all current matters of interest in science, as well as in engineering. One by one his old friends died--Black in 1799, Priestley, an exile to America, in 1803, and Robison a little later. Boulton died, at the age of eighty-one, August 17, 1809, and even the loss of this nearest and dearest of his friends outside the family was a less severe blow than that of his son Gregory, who died in 1804.

Yet the great engineer and inventor was not depressed by the loneliness which was gradually coming upon him. He wrote: "I know that all men must die, and I submit to the decrees of Nature, I hope, with due reverence to the Disposer of events;" and neglected no opportunity to secure amusement or instruction, and kept body and mind constantly occupied. He still attended the weekly meetings of the club, meeting Rennie and Telford, and other distinguished men of his own and the succeeding generation. He lost nothing of his fondness for invention, and spent many months in devising a machine for copying statuary, which he had not perfected to his own satisfaction at the time of his death, ten years later. This machine was a kind of pentagraph, which could be worked in any plane, and in which the marking-pencil gave place to a cutting-tool. The tracing-point followed the surface of the pattern, while the cutting-point, following its motion precisely, formed a fac-simile in the material operated upon.

In the year 1800 he invented the water-main which was laid down by the Glasgow Water-Works Company across the Clyde. The joints were spherical and articulated, like those of the lobster's tail.

His workshop, of which a sketch is hereafter given, as drawn by the artist Skelton, was in the garret of his house, and was well supplied with tools and all kinds of laboratory material. His lathe and his copying-machine were placed before the window, and his writing-desk in the corner. Here he spent the greater part of his leisure time, often even taking his meals in the little shop, rather than go to the table for them. Even when very old, he occasionally made a journey to London or Glasgow, calling on his old friends and studying the latest engineering devices and inspecting public works, and was everywhere welcomed by young and old as the greatest living engineer, or as the kind and wise friend of earlier days.

He died August 19, 1819, in the eighty-third year of his age, and was buried in Handsworth Church. The sculptor Chantrey was employed to place a fitting monument above his grave, and the nation erected a statue of the great man in Westminster Abbey.

This sketch of the greatest of all the inventors of the steam-engine has been given no greater length than its subject justifies. Whether we consider Watt as the inventor of the standard steam-engine of the nineteenth century, as the scientific investigator of the physical principles upon which the invention is based, or as the builder and introducer of the most powerful known instrument by which the "great sources of power in Nature are converted, adapted, and applied for the use and convenience of man," he is fully entitled to preeminence. His character as a man was no less admirable than as an engineer.

Smiles, Watt's most conscientious and indefatigable biographer, writes:[41]

[41] "Life of Watt," p. 512.

"Some months since, we visited the little garret at Heathfield in which Watt pursued the investigations of his later years. The room had been carefully locked up since his death, and had only once been swept out. Everything lay very much as he left it. The piece of iron which he was last employed in turning, lay on the lathe. The ashes of the last fire were in the grate; the last bit of coal was in the scuttle. The Dutch oven was in its place over the stove, and the frying-pan in which he cooked his meals was hanging on its accustomed nail. Many objects lay about or in the drawers, indicating the pursuits which had been interrupted by death--busts, medallions, and figures, waiting to be copied by the copying-machine--many medallion-moulds, a store of plaster-of-Paris, and a box of plaster casts from London, the contents of which do not seem to have been disturbed. Here are Watt's ladles for melting lead, his foot-rule, his glue-pot, his hammer. Reflecting mirrors, an extemporized camera with the lenses mounted on pasteboard, and many camera-glasses laid about, indicate interrupted experiments in optics. There are quadrant-glasses, compasses, scales, weights, and sundry boxes of mathematical instruments, once doubtless highly prized. In one place a model of the governor, in another of the parallel-motion, and in a little box, fitted with wooden cylinders mounted with paper and covered with figures, is what we suppose to be a model of his calculating-machine. On the shelves are minerals and chemicals in pots and jars, on which the dust of nearly half a century has settled. The moist substances have long since dried up; the putty has been turned to stone, and the paste to dust. On one shelf we come upon a dish in which lies a withered bunch of grapes. On the floor, in a corner, near to where Watt sat and worked, is a hair-trunk--a touching memorial of a long-past love and a long-dead sorrow. It contains all poor Gregory's school-books, his first attempts at writing, his boy's drawings of battles, his first school-exercises down to his college-themes, his delectuses, his grammars, his dictionaries, and his class-books--brought into this retired room, where the father's eye could rest upon them. Near at hand is the sculpture-machine, on which he continued working to the last. Its wooden frame is worm-eaten, and dropping into dust, like the hands that made it. But though the great workman is gone to rest, with all his griefs and cares, and his handiwork is fast crumbling to decay, the spirit of his work, the thought which he put into his inventions, still survives, and will probably continue to influence the destinies of his race for all time to come."

The visitor to Westminster Abbey will find neither monarch, nor warrior, nor statesman, nor poet, honored with a nobler epitaph than that which is inscribed on the pedestal of Chantrey's monument to Watt:

NOT TO PERPETUATE A NAME,
WHICH MUST ENDURE WHILE THE PEACEFUL ARTS FLOURISH,
BUT TO SHOW
THAT MANKIND HAVE LEARNT TO HONOR THOSE WHO BEST DESERVE THEIR
GRATITUDE,
THE KING,
HIS MINISTERS, AND MANY OF THE NOBLES AND COMMONERS OF THE REALM,
RAISED THIS MONUMENT TO
JAMES WATT,
WHO, DIRECTING THE FORCE OF AN ORIGINAL GENIUS,
EARLY EXERCISED IN PHILOSOPHIC RESEARCH,
TO THE IMPROVEMENT OF
THE STEAM-ENGINE,
ENLARGED THE RESOURCES OF HIS COUNTRY, INCREASED THE POWER OF MAN,
AND ROSE TO AN EMINENT PLACE
AMONG THE MOST ILLUSTRIOUS FOLLOWERS OF SCIENCE AND THE REAL
BENEFACTORS OF THE WORLD.

BORN AT GREENOCK, MDCCXXXVI.

DIED AT HEATHFIELD, IN STAFFORDSHIRE, MDCCCXIX.