A History of the Growth of the Steam-Engine Part 10

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 s.p.a.ce, _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 pa.s.sing from the engine into the s.p.a.ce, _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valve-gear was subsequently greatly improved by Murdoch, Watt's ingenious and efficient foreman, but it is now entirely superseded on engines of this cla.s.s by the eccentric, and the various forms of valve-gear driven by it.

[Ill.u.s.tration: FIG. 33.--Watt's Half-Trunk Engine, 1784.]

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.

[Ill.u.s.tration: FIG. 34.--The Watt Hammer, 1784.]

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 c.o.c.k, 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 a.s.sistants, 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 const.i.tuents. 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 copartners.h.i.+p 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 pa.s.sed 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 amus.e.m.e.nt 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 ent.i.tled 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.

[Ill.u.s.tration: FIG. 35.--James Watt's Workshop. (From Smiles's "Lives of Boulton and Watt.")]

"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-gla.s.ses laid about, indicate interrupted experiments in optics. There are quadrant-gla.s.ses, compa.s.ses, 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 cla.s.s-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 n.o.bler 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 GRAt.i.tUDE, THE KING, HIS MINISTERS, AND MANY OF THE n.o.bLES 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 ILl.u.s.tRIOUS FOLLOWERS OF SCIENCE AND THE REAL BENEFACTORS OF THE WORLD.

BORN AT GREENOCK, MDCCx.x.xVI.

DIED AT HEATHFIELD, IN STAFFORDs.h.i.+RE, MDCCCXIX.

[Ill.u.s.tration: Tomb of James Watt.]

SECTION II.--THE CONTEMPORARIES OF JAMES WATT.

In the chronology of the steam-engine, the contemporaries of Watt have been so completely overshadowed by the greater and more successful inventor, as to have been almost forgotten by the biographer and by the student of history. Yet, among the engineers and engine-builders, as well as among the inventors of his day, Watt found many enterprising rivals and keen compet.i.tors. Some of these men, had they not been so completely fettered by Watt's patents, would have probably done work which would have ent.i.tled them to far higher honor than has been accorded them.

WILLIAM MURDOCH was one of the men to whom Watt, no less than the world, was greatly indebted. For many years he was the a.s.sistant, friend, and coadjutor of Watt; and it is to his ingenuity that we are to give credit for not only many independent inventions, but also for the suggestions and improvements which were often indispensable to the formation and perfection of some of Watt's own inventions.

Murdoch was employed by Boulton & Watt in 1776, and was made superintendent of construction in the engine department, and given general charge of the erection of engines. He was sent into Cornwall, and spent in that district much of the time during which he served the firm, erecting pumping-engines, the construction of which for so many years const.i.tuted a large part of the business of the Soho establishment. He was looked upon by both Boulton and Watt as a sincere friend, as well as a loyal adherent, and from 1810 to 1830 was given a partner's share of the income of the firm, and a salary of 1,000. He retired from business at the last of the two dates named, and, dying in 1839, was buried near the two partners in Handsworth Church.

Murdoch made a model, in 1784, of the locomotive patented by Watt in that year. He devised the arrangement of "sun-and-planet wheels,"

adopted for a time in all of Watt's "rotative" engines, and invented the oscillating steam-engine (Fig. 36) in 1785, using the "D-slide valves," _G_, moved by the gear, _E_, which was driven by an eccentric on the shaft, without regard to the oscillation of the cylinder, _A_.

He was the inventor of a rotary engine and of many minor machines for special purposes, and of many machine-tools used at Soho in building engines and machines. He seems, like Watt, to have had special fondness for the worm-gear, and introduced it wherever it could properly take the place of ordinary gearing. Some of the machines designed by Watt and Murdoch, who always worked well together, were found still in use and in good working condition by the author when visiting the works at Soho in 1873. The old mint in which, from 1797 to 1805, Boulton had coined 4,000 tons of copper, had then been pulled down, and a new mint had been erected in 1860. Many old machines still remained about the establishment as souvenirs of the three great mechanics.

[Ill.u.s.tration: FIG. 36.--Murdoch's Oscillating Engine, 1785.]

Outside of Soho, Murdoch also found ample employment for his inventive talent. In 1792, while at Redruth, his residence before finally returning to Soho, he was led to speculate upon the possibility of utilizing the illuminating qualities of coal-gas, and, convinced of its practicability, he laid the subject before the Royal Society in 1808, and was awarded the Rumford gold medal. He had, ten years earlier, lighted a part of the Soho works with coal-gas, and in 1803 Watt authorized him to extend his pipes throughout all the buildings.

Several manufacturers promptly introduced the new light, and its use extended very rapidly.

Still another of Murdoch's favorite schemes was the transmission of power by the use of compressed air. He drove the pattern-shop engine at Soho by means of air from the blowing-engine in the foundery, and erected a pneumatic lift to elevate castings from the foundery-floor to the ca.n.a.l-bank. He made a steam-gun, introduced the heating of buildings by the circulation of hot water, and invented the method of transmitting packages through tubes by the impulse of compressed air, as now practised by the "pneumatic dispatch" companies. He died at the age of eighty-five years.

Among the most active and formidable of Watt's business rivals was JONATHAN HORNBLOWER, the patentee of the "compound" or double-cylinder engine. A sketch of this engine, as patented by Hornblower in 1781, is here given (Fig. 37). It was first described by the inventor in the "Encyclopaedia Britannica." It consists, as is seen by reference to the engraving, of two steam-cylinders, _A_ and _B_--_A_ being the low and _B_ the high pressure cylinder--the steam leaving the latter being exhausted into the former, and, after doing its work there, pa.s.sing into the condenser, as already described. The piston-rods, _C_ and _D_, are both connected to the same part of the beam by chains, as in the other early engines. These rods pa.s.s through stuffing-boxes in the cylinder-heads, which are fitted up like those seen on the Watt engine. Steam is led to the engine through the pipe, _G Y_, and c.o.c.ks, _a_, _b_, _c_, and _d_, are adjustable, as required, to lead steam into and from the cylinders, and are moved by the plug-rod, _W_, which actuates handles not shown. _K_ is the exhaust-pipe leading to the condenser. _V_ is the engine feed-pump rod, and _X_ the great rod carrying the pump-buckets at the bottom of the shaft.

The c.o.c.ks _c_ and _a_ being open and _b_ and _d_ shut, the steam pa.s.ses from the boiler into the upper part of the steam-cylinder, _B_; and the communication between the lower part of _B_ and the top of _A_ is also open. Before starting, steam being shut off from the engine, the great weight of the pump-rod, _X_, causes that end of the beam to preponderate, the pistons standing, as shown, at the top of their respective steam-cylinders.

The engine being freed from all air by opening all the valves and permitting the steam to drive it through the engine and out of the condenser through the "snifting-valve," _O_, the valves _b_ and _d_ are closed, and the c.o.c.k in the exhaust-pipe opened.

[Ill.u.s.tration: FIG. 37.--Hornblower's Compound Engine, 1781.]

The steam beneath the piston of the large cylinder is immediately condensed, and the pressure on the upper side of that piston causes it to descend, carrying that end of the beam with it, and raising the opposite end with the pump-rods and their attachments. At the same time, the steam from the lower end of the small high-pressure cylinder being let into the upper end of the larger cylinder, the completion of the stroke finds a cylinder full of steam transferred from the one to the other with corresponding increase of volume and decrease of pressure. While expanding and diminis.h.i.+ng in pressure as it pa.s.ses from the smaller into the larger cylinder, this charge of steam gradually resists less and less the pressure of the steam from the boiler on the upper side of the piston of the small cylinder, _B_, and the net result is the movement of the engine by pressures exerted on the upper sides of both pistons and against pressures of less intensity on the under sides of both. The pressures in the lower part of the small cylinder, in the upper part of the large cylinder, and in the communicating pa.s.sage, are evidently all equal at any given time.

When the pistons have reached the bottoms of their respective cylinders, the valves at the top of the small cylinder, _B_, and at the bottom of the large cylinder, _A_, are closed, and the valves _c_ and _d_ are opened. Steam from the boiler now enters beneath the piston of the small cylinder; the steam in the larger cylinder is exhausted into the condenser, and the steam already in the small cylinder pa.s.ses over into the large cylinder, following up the piston as it rises.

Thus, at each stroke a small cylinder full of steam is taken from the boiler, and the same weight, occupying the volume of the larger cylinder, is exhausted into the condenser from the latter cylinder.

Referring to the method of operation of this engine, Prof. Robison demonstrated that the effect produced was the same as in Watt's single-cylinder engine--a fact which is comprehended in the law enunciated many years later by Rankine, that, "so far as the theoretical action of the steam on the piston is concerned, it is immaterial whether the expansion takes place in one cylinder, or in two or more cylinders." It was found, in practice, that the Hornblower engine was no more economical than the Watt engine; and that erected at the Tin Croft Mine, Cornwall, in 1792, did even less work with the same fuel than the Watt engines.

Hornblower was prosecuted by Boulton & Watt for infringement. The suit was decided against him, and he was imprisoned in default of payment of the royalty, and fine demanded. He died a disappointed and impoverished man. The plan thus unsuccessfully introduced by Hornblower was subsequently modified and adopted by others among the contemporaries of Watt; and, with higher steam and the use of the Watt condenser, the "compound" gradually became a standard type of steam-engine.

Arthur Woolf, in 1804, re-introduced the Hornblower or Falck engine, with its two steam-cylinders, using steam of higher tension. His first engine was built for a brewery in London, and a considerable number were subsequently made. Woolf expanded his steam from six to nine times, and the pumping-engines built from his plans were said to have raised about 40,000,000 pounds one foot high per bushel of coals, when the Watt engine was raising but little more than 30,000,000. In one case, a duty of 57,000,000 was claimed.

The most successful of those compet.i.tors of Watt who endeavored to devise a peculiar form of pumping-engine, which should have the efficiency of that of Boulton & Watt, and the necessary advantage in first cost, were WILLIAM BULL and RICHARD TREVITHICK.[42] The accompanying ill.u.s.tration shows the design, which was then known as the "Bull Cornish Engine."

[42] For an exceedingly interesting and very faithful account of their work, _see_ "Life of Richard Trevithick," by F. Trevithick, London, 1872.