(38.)

Fig. 14.

Newcomen resumed the old method of raising the water from the mines by ordinary pumps, but conceived the idea of working these pumps by some moving power less expensive than that of horses. The means whereby he proposed effecting this, was by connecting the end of the pump-rodD(fig.14.) by a chain with the arch headAof a[Pg066]working-beamA B, playing on an axisC. The other arch headBof this beam was connected by a chain with the rodEof a solid pistonP, which moved air-tight in a cylinderF. If a vacuum be created beneath the pistonP, the atmospheric pressure acting upon it will press it down with a force of fifteen pounds per square inch; and the endAof the beam being thus raised, the pump-rodDwill be drawn up. If a pressure equivalent to the atmosphere be then introduced below the piston, so as to neutralise the downward pressure, the piston will be in a state of indifference as to the rising or falling; and if in this case the rodDbe made heavier than the piston and its rod, so as to overcome the friction, it will descend, and elevate the piston again to the top of the cylinder. The vacuum being again produced, another descent of the piston, and consequent elevation of the pump-rod, will take place; and so the process may be continued.

Such was Newcomen's first conception of theatmospheric engine; and the contrivance had much, even at the first view, to recommend it. The power of such a machine would depend entirely on the magnitude of the piston; and being independent of highly elastic steam, would not expose the materials to the destructive heat which was necessary for working Savery's engine. Supposing a perfect vacuum to be produced under the piston in the cylinder, an effective downward pressure would be obtained, amounting to fifteen times as many pounds as there are square inches in the section of the piston.[12]Thus, if the base of the piston were 100 square inches, a pressure equal to 1500 pounds would be obtained.

(38.)In order to accomplish this, two things were necessary: 1. To make a speedy and effectual vacuum below the[Pg067]piston in the descent; and, 2. To contrive a counterpoise for the atmosphere in the ascent.

The condensation of steam immediately presented itself as the most effectual means of accomplishing the former; and the elastic force of the same steam previous to condensation an obvious method of effecting the latter. Nothing now remained to carry the design into execution, but the contrivance of means for the alternate introduction and condensation of the steam; and Newcomen and Cawley were accordingly granted a patent in 1707, in which Savery was united, in consequence of the principle of condensation for which he had previously received a patent being necessary to the projected machine. We shall now describe theatmospheric engine, as first constructed by Newcomen:—

The boilerK(fig.14.) is placed over a furnaceI, the flue of which winds round it, so as to communicate heat to every part of the bottom of it. In the top, which is hemispherical, two gauge-cocksG G′are placed, as in Savery's engine, and apuppet valveV, which opens upward, and is loaded at one pound per square inch; so that when the steam produced in the boiler exceeds the pressure of the atmosphere by more than one pound on the square inch, the valveVis lifted, and the steam escapes through it, and continues to escape until its pressure is sufficiently diminished, when the valveVagain falls into its seat. This valve performs the office of the safety-valve in modern engines.

The great steam-tube is represented atS, which conducts steam from the boiler to the cylinder; and a feeding pipeT, furnished with a cock, which is opened and closed at pleasure, proceeds from a cisternLto the boiler. By this pipe the boiler may be replenished from the cistern, when the gauge cockG′indicates that the level has fallen below it. The cisternLis supplied with hot water, by means which we shall presently explain.

(39.)To understand the mechanism necessary to work the piston, let us consider how the supply and condensation of steam must be regulated. When the piston has been forced to the bottom of the cylinder by the atmospheric pressure acting against a vacuum, in order to balance that pressure,[Pg068]and enable it to be drawn up by the weight of the pump-rod, it is necessary to introduce steam from the boiler. This is accomplished by opening the cockRin the steam pipeS. The steam being thus introduced from the boiler, its pressure balances the action of the atmosphere upon the piston, which is immediately drawn to the top of the cylinder by the weight of the pump-rodD. It then becomes necessary to condense this steam, in order to produce a vacuum. To accomplish this, the further supply of steam must be cut off, which is done by closing the cockR. The supply of steam from the boiler being thus suspended, the application of cold water on the external surface of the cylinder becomes necessary to condense the steam within it. This was done by enclosing the cylinder within another, leaving a space between them.[13]Into this space cold water was allowed to flow from a cockMplaced over it, supplied by a pipe from the cisternN. This cistern is supplied with water by a pumpO, which is worked by the engine.

The cold water supplied fromM, having filled the space between the two cylinders, abstracts the heat from the inner one; and condensing the steam, produces a vacuum, into which the piston is forced by the atmospheric pressure. Preparatory to the next descent, the water which thus fills the space between the cylinders, and which is warmed by the heat abstracted from the steam, must be discharged, in order to give room for a fresh supply of cold water fromM. An aperture, furnished with a cock, is accordingly provided in the bottom of the cylinder, through which the water is discharged into the cisternL; and being warm, is adapted for the supply of the boiler throughT, as already mentioned.

The cockRbeing now again opened, steam is admitted below the piston, which, as before, ascends, and the descent is again accomplished by closing the cockR, and opening the cockM, admitting cold water between the cylinders, and thereby condensing the steam below the piston.

The condensed steam, thus reduced to water, will collect[Pg069]in the bottom of the cylinder, and resist the descent of the piston. It is therefore necessary to provide an exit for it, which is done by a valve openingoutwardsinto a tube which leads to the feeding cisternL, into which the condensed steam is driven.

That the piston should continue to be air-tight, it was necessary to keep a constant supply of water over it; this was done by a cock similar toM, which allowed water to flow from the pipe M on the piston.

(40.)Soon after the first construction of these engines, an accidental circumstance suggested to Newcomen a much better method of condensation than the application of cold water on the external surface of the cylinder. An engine was observed to work several strokes with unusual rapidity, and without the regular supply of the condensing water. Upon examining the piston, a hole was found in it, through which the water, which was poured on to keep it air-tight, flowed, and instantly condensed the steam under it.

On this suggestion Newcomen abandoned the external cylinder, and introduced a pipeH, furnished with a cockQ, into the bottom of the cylinder, so that, on turning the cock, the pressure of the water in the pipeH, from the level of the water in the cisternN, would force the water to rise as a jet into the cylinder, and would instantly condense the steam. This method of condensing by injection formed a very important improvement in the engine, and is still used.

(41.)Having taken a general view of the parts of the atmospheric engine, let us now consider more particularly its operation.

When the engine is not working, the weight of the pump-rodD(fig.14.) draws down the beamA, and draws the piston to the top of the cylinder, where it rests. Let us suppose all the cocks and valves closed, and the boiler filled to the proper depth. The fire being lighted beneath it, the water is boiled until the steam acquires sufficient force to lift the valveV. When this takes place, the engine may be started. For this purpose the regulating valveRis opened. The steam rushes in, and is first condensed by the cold cylinder. After a short time the cylinder acquires the temperature of the steam, which then[Pg070]ceases to be condensed, and mixes with the air which filled the cylinder. The steam and heated air, having a greater force than the atmospheric pressure, will open a valve placed at the endXof a small tube in the bottom of the cylinder, and which opens outwards. From this (which is called theblowing valve[14]) the steam and air rush in a constant stream, until all the air has been expelled, and the cylinder is filled with the pure vapour of water. This process is calledblowingthe engine preparatory to starting it.

When it is about to be started, the engine-man closes the regulatorR, and thereby suspends the supply of steam from the boiler. At the same time he opens thecondensing valveH[15]; and thereby throws up a jet of cold water into the cylinder. This immediately condenses the steam contained in the cylinder, and produces the vacuum. (The atmosphere cannot enter theblowingvalve, because it opensoutwards, so that no air can enter to vitiate the vacuum.) The atmospheric pressure above the piston now takes effect, and forces it down in the cylinder. The descent being completed, the engine-man closes the condensing valveH, and opens the regulator,R. By this means he stops the play of the jet within the cylinder, and admits the steam from the boiler. The first effect of the steam is to expel the condensing water and condensed steam which are collected in the bottom of the cylinder, through the tubeY, containing a valve which opensoutwards(called theeduction valve), which leads to the hot cisternL, into which this water is therefore discharged.

When the steam admitted throughRceases to be condensed, it balances the atmospheric pressure above the piston, and thus permits it to be drawn to the top of the cylinder by the weight of the rodD. This ascent of the piston is also assisted by the circumstance of the steam being somewhat stronger than the atmosphere.

When the piston has reached the top, the regulating valveRis closed, and the condensing valveHopened, and another descent produced, as before, and so the process is continued.[Pg071]

The manipulation necessary in working this engine was, therefore, the alternate opening and closing of two valves; the regulating and condensing valves. When the piston reached the top of the cylinder, the former was to be closed, and the latter opened; and, on reaching the bottom, the former was to be opened, and the latter closed.

(42.)The duty of working the engine requiring no great amount of labour, or skill, was usually entrusted to boys, called,cock boys. It happened that one of the most important improvements which has ever been made in the working of steam engines was due to the ingenuity of one of these boys. It is said that a lad, namedHumphrey Potter, was employed to work the cocks of an atmospheric engine, and being tempted to escape from the monotonous drudgery to which his duty confined him, his ingenuity was sharpened so as to prompt him to devise some means by which he might indulge his disposition to play without exposing himself to the consequences of suspending the performance of the engine. On observing the alternate ascending and descending motion of the beam above him, and considering it in reference to the labour of his own hands, in alternately raising and lowering the levers which governed the cocks, he perceived a relation which served as a clue to a simple contrivance, by which the steam engine, for the first time, became an automaton. When the beam arrived at the top of its play, it was necessary to open the steam valve by raising a lever, and to close the injection valve by raising another. This he saw could be accomplished by attaching strings of proper length to these levers, and tying them to some part of the beam. These levers required to be moved in the opposite direction when the beam attained the lowest point of its play. This he saw could be accomplished by strings, either connected with the outer arm of the beam, or conducted over rods or pulleys. In short, he contrived means of so connecting the levers which governed the two cocks by strings with the beam, that the beam opened and closed these cocks with the most perfect regularity and certainty as it moved upwards and downwards.

Besides rendering the machine independent of manual[Pg072]superintendence, this process conferred upon it much greater regularity of performance than any manual superintendence could ensure.

This contrivance of Potter was very soon improved by the substitution of a bar, called aplug frame, which was suspended from the arm of the beam, and which carried upon it pins, by which the arms of the levers governing the cocks were struck as the plug-frame ascended and descended, so as to be opened and closed at the proper times.

The engine thus improved required no other attendance except to feed the boiler occasionally by the cockT, and to attend the furnace.

(43.)However the merit of the discovery of the physical principles on which the mechanical application of steam depends may be awarded, it must be admitted that the engine contrived by Newcomen and his associates, considered as a practical machine, was immeasurably superior to that which preceded it; superior, indeed, to such a degree, that while the one was incapable of any permanently useful application, the other soon became a machine of extensive utility in the drainage of mines; and, even at the present time, the atmospheric engine is not unfrequently used in preference to the modern steam engine, in districts where fuel is abundant and cheap; the expense of constructing and maintaining it being considerably less than that of an improved steam engine. The low pressure of the steam used in working it, rendered it perfectly safe. While Savery's engine, to work with effect, required that the steam confined in the vessels should have a bursting pressure amounting to about thirty pounds per square inch, the pressure of steam in the boiler and cylinder of the atmospheric engine required only a pressure about one pound per square inch. The high pressure also of the steam used in Savery's engine, was necessarily accompanied, as we shall presently explain, by a greatly increased temperature. The effect of this was, to weaken and gradually destroy the vessels, especially those which, like the steam vesselsVandV′(fig.12.), were alternately heated and cooled.

Besides these defects, the power of Savery's engines was[Pg073]also very restricted, both as to the quantity of water raised and as to the height to which it was elevated. On the other hand, the atmospheric engine was limited in its power only by the dimensions of its piston. Another considerable advantage which the atmospheric engine possessed over that of Savery, was the facility with which it was capable of driving machinery by means of the working-beam. The merit, however, of Newcomen's engine, regarded as an invention, and apart from merely practical considerations, must be ascribed principally to its mechanism and combinations. We find in it no new principle, and scarcely even a novel application of a principle. The agency of the atmospheric pressure acting against a vacuum, or partial vacuum, had been long known: the method of producing a vacuum by the condensation of steam had been suggested by Papin, and carried into practical effect by Savery. The mechanical power obtained from the direct pressure of the elastic force of steam, used in the atmospheric engine to balance the atmosphere during the ascent of the piston, was suggested by De Caus and Lord Worcester. The boiler, gauge pipes, and the regulator, were all borrowed from the engine of Savery. The idea of using the atmospheric pressure against a vacuum or partial vacuum, to work a piston in a cylinder, had been suggested by Otto Guericke, an ingenious German philosopher, who invented the air-pump; and this, combined with the production of a vacuum by the condensation of steam, was subsequently suggested by Papin. The use of a working-beam could not have been unknown. Nevertheless, the judicious combination of these scattered principles must be acknowledged to deserve considerable credit. In fact, the mechanism contrived by Newcomen rendered a machine which was before altogether inefficient, highly efficient: and, as observed by Tredgold, such a result, considered in a practical sense, should be more highly valued than the fortuitous discovery of a physical principle. The method of condensing the steam by the sudden injection of water, and of expelling the air and water from the cylinder by the injection of steam, are two contrivances not before in use, which are quite essential to the[Pg074]effective operation of the engine. These processes, which are still necessary to the operation of the improved steam engine, appear to be wholly due to the inventors of the atmospheric engine.

ATMOSPHERIC ENGINE.

FOOTNOTES:[9]This pipe is represented as proceeding from the force-pipe above the cisternC, in the perspective view of Savery's engine at the head of this chapter.[10]Hot water being lighter than cold, floats on the surface.[11]"Captain" is a title given in Cornwall to the superintendent of the works connected with a mine.[12]As the calculation of the power of an engine depends on the number of square inches in the section of the piston, it may be useful to give a rule for computing the number of square inches in a circle. The following rule will always give the dimensions with sufficient accuracy:—Multiply the number of inches in the diameter by itself; divide the product by 14, and multiply the quotient thus obtained by 11, and the result will be the number of square inches in the circle. Thus, if there be 12 inches in the diameter, this multiplied by itself gives 144, which divided by 14 gives104⁄44,which multiplied by 11 gives 115, neglecting fractions. There are, therefore, 115 square inches in a circle whose diameter is 12 inches.[13]The external cylinder is not represented in the diagram.[14]Also called thesniftingvalve, from the peculiar noise made by the air and steam escaping from it.[15]Also called theinjection valve.

[9]This pipe is represented as proceeding from the force-pipe above the cisternC, in the perspective view of Savery's engine at the head of this chapter.

[10]Hot water being lighter than cold, floats on the surface.

[11]"Captain" is a title given in Cornwall to the superintendent of the works connected with a mine.

[12]As the calculation of the power of an engine depends on the number of square inches in the section of the piston, it may be useful to give a rule for computing the number of square inches in a circle. The following rule will always give the dimensions with sufficient accuracy:—Multiply the number of inches in the diameter by itself; divide the product by 14, and multiply the quotient thus obtained by 11, and the result will be the number of square inches in the circle. Thus, if there be 12 inches in the diameter, this multiplied by itself gives 144, which divided by 14 gives104⁄44,which multiplied by 11 gives 115, neglecting fractions. There are, therefore, 115 square inches in a circle whose diameter is 12 inches.

[13]The external cylinder is not represented in the diagram.

[14]Also called thesniftingvalve, from the peculiar noise made by the air and steam escaping from it.

[15]Also called theinjection valve.

GREENOCK, IN 1824.

[Pg075]TOCINX

PROGRESS OF THE ATMOSPHERIC ENGINE.—SMEATON'S IMPROVEMENTS.—BRINDLEY, ENGINEER OF THE BRIDGEWATER CANAL.—INVENTS THE SELF-REGULATING FEEDER.—JAMES WATT.—HIS DESCENT AND PARENTAGE.—ANECDOTES OF HIS BOYHOOD.—HIS EARLY ACQUIREMENTS.—GOES TO LONDON.—RETURNS TO GLASGOW.—IS APPOINTED INSTRUMENT-MAKER TO THE UNIVERSITY.—OPENS A SHOP IN GLASGOW.—HIS FRIENDS AND PATRONS.—ADAM SMITH.—DR. BLACK.—ROBERT SIMSON.—PROFESSOR ROBISON.—WATT'S PERSONAL CHARACTER.—INDUSTRIOUS AND STUDIOUS HABITS.—HIS ATTENTION FIRST DIRECTED TO STEAM.—EXPERIMENTS ON HIGH-PRESSURE STEAM.—REPAIRS AN ATMOSPHERIC MODEL.—EXPERIMENTAL INQUIRY CONSEQUENT ON THIS.—ITS RESULTS.—DISCOVERS THE GREAT DEFECTS OF THE ATMOSPHERIC ENGINE.—DISCOVERY BY EXPERIMENT OF THE EXPANSION WHICH WATER UNDERGOES IN EVAPORATION.—DISCOVERS THE LATENT HEAT OF STEAM.—IS INFORMED BY DR. BLACK OF THE THEORY OF LATENT HEAT.

(44.)The atmospheric engine was brought to a state of considerable efficiency and improvement by Mr. Beighton, in 1718. From that time it continued in use without any change in its[Pg076]principle, and with little improvement in its structure, for half a century. Although engines of this kind continued to be extensively constructed, they were usually executed by ordinary mechanics, incapable of applying to them the just principles of practical science; and, consequently, little attention was paid to their proportions. It was not until about the year 1772, that Mr. John Smeaton, the celebrated engineer, applied the powers of his mind to the investigation of this machine, as he had previously done with such success to wind and water mills. Although he did not introduce any new principle into the atmospheric engine, yet it derived greatly augmented power from the proportions which he established for engines of different magnitudes.

In 1759, Mr. James Brindley, whose name is so celebrated as the engineer of the Duke of Bridgewater's canal, obtained a patent for some improvements in the atmospheric engine. He proposed that the boiler should be made of wood and stone, with a stove or fire-place of cast iron within it, so that the fire should be surrounded on every side by water. The chimney was to be an iron pipe or tube, conducted through the boiler; so that the heated air, in passing from the fire, should impart a portion of its heat to the water. He also proposed a method of feeding the boiler, which, by self-acting machinery, would keep the water in the boiler at a fixed level, independently of any attention on the part of the engine-man. This was to be accomplished by a buoy or float upon the surface of the water in the boiler, which should communicate with a valve in the feed-pipe, so that when the level of the water in the boiler fell, the float or buoy, falling with it, would open the valve and supply the feed. It is stated, in theBiographia Britannica, that Mr. Brindley, in 1756, undertook to erect an engine at Newcastle-under-Lyne; but he is said to have been discouraged by the obstacles which were thrown in his way, and to have abandoned the steam engine.

The interval between the invention of the atmospheric engine, and the amelioration it received at the hands of Smeaton, has been rendered memorable by the advent of one who was destined to work a mighty change in the condition[Pg077]of the human race by the application of his vast genius to the adaptation of steam power to the uses of life.

(45.)James Wattwas born at Greenock, in Scotland, on the nineteenth day of January, in the year 1736.[16]

The great-grandfather of Watt, a farmer in Aberdeenshire, was killed in one of the battles of Montrose. The victorious party, not thinking death a sufficient expiation for the political opinions in support of which he had fought and bled, punished him in the person of his son, by confiscating his little property. Thomas Watt, the son, thus deprived of support, was received by distant relations, and, for a time, applied himself to study, by which he was enabled, after the restoration of tranquillity, to establish himself at Greenock as a teacher of practical mathematics and navigation. He resided in the burgh or barony of Crawford's Dyke, and attained a position of sufficient respectability to be elected to the office of baron-baillie, or chief magistrate, and died in 1734, at the advanced age of ninety-two years.

Thomas Watt had two sons. The elder, John, adopted the profession of his father, and was a teacher of mathematics and navigation at Glasgow: he died in 1737, at the age of fifty years. The second son, James, the father of the celebrated engineer, was, during a quarter of a century, treasurer of the town council of Greenock, and a local magistrate. He was remarked for the ardent zeal and enlightened spirit with which he discharged his public duties. His business was that of a ship-chandler, builder, and general merchant; but, unhappily, notwithstanding his active industry, he lost, in the decline of his life, by unsuccessful commercial speculations, a part of the property which he had so honourably acquired. He died in 1782, at the age of eighty-four years.

James Watt, to whom the world is so largely indebted for the extension and improvement of steam power, had from his birth an extremely delicate constitution. From his mother,[Pg078]whose family name was Muirhead, he received his first lessons in reading, and he learned from his father writing and arithmetic. Although he was entered as a pupil in the grammar school of Greenock, yet such was his delicate state of health, that his attendance there was so interrupted by constant indisposition that he could derive but little benefit from the opportunities of instruction which it afforded. For a great period of the year he was confined to his room, where he devoted himself to study without the aid of instruction. It was in the retirement of the sick chamber that the high intellectual faculties of Watt, which were destined to produce such precious fruits, began to unfold themselves. He was too sickly to be subjected to the restraints which the business of education usually imposes on children. His parents, therefore, found it necessary to leave him at liberty to choose his occupations and amusements. The following anecdotes will show the use he made of this freedom.

A friend of his father found the boy one day stretched upon the hearth tracing with chalk various lines and angles. "Why do you permit this child," said he, "to waste his time so; why not send him to school?" Mr. Watt replied, "You judge him hastily; before you condemn us, ascertain how he is employed." On examining the boy, then six years of age, it was found that he was engaged in the solution of a problem of Euclid!

Having observed the tendency of his son's mind, Mr. Watt placed at his disposal a collection of tools. These he soon learned to use with the greatest skill. He took to pieces and put together, again and again, all the children's toys which he could procure; and he was constantly employed in making new ones. Subsequently he used his tools in constructing a little electrical machine, the sparks proceeding from which became a great subject of amusement to all the playfellows of the poor invalid.

Though endowed with great retentive powers, Watt would probably never have figured among the prodigies of a common school: he would have been slow to commit his lessons to memory, from the repugnance which he would feel to repeat like a parrot anything which he did not perfectly[Pg079]understand. The natural tendency of his mind to meditate on whatever came before it, would give him, to superficial observers, the appearance of dullness. Happily, however, he had a parent who was sufficiently clear-sighted, and who entertained high hopes of the growing faculties of his son. More distant and less sagacious relations were not so sanguine. One day Mrs. Muirhead, the aunt of the boy, reproaching him for what she conceived to be listless idleness, desired him to take a book and occupy himself usefully. "More than an hour has now passed away," said she, "and you have not uttered a single word. Do you know what you have been doing all this time? You have taken off, and put on, repeatedly, the lid of the tea-pot; you have been holding the saucers and the spoons over the steam, and you have been endeavouring to catch the drops of water formed on them by the vapour. Is it not a shame for you to waste your time so?"

Mrs. Muirhead was little aware that this was the first experiment in the splendid career of discovery which was subsequently to immortalise her little nephew. She did not see, as we now can, in the little boy playing with the tea-pot, the great engineer preluding to those discoveries which were destined to confer on mankind benefits so inestimable.

One of the social qualities of mind which was remarkable throughout his life, was the singular felicity and grace with which he related anecdotes. This power was manifested even in his earliest childhood. The following is an extract from a letter written by Mrs. Marion Campbell, his cousin, and the playfellow of his childhood:—

"He was not fourteen when his mother brought him to Glasgow to visit a friend of hers; his brother John accompanied him. On Mrs. Watt's return to Glasgow, some weeks after, her friend said, 'You must take your son James home; I cannot stand the degree of excitement he keeps me in; I am worn out for want of sleep. Every evening before ten o'clock, our usual hour of retiring to rest, he contrives to engage me in conversation, then begins some striking tale, and, whether humorous or pathetic, the interest is so overpowering that the family all listen to him with breathless attention, and hour after hour strikes unheeded.'"[Pg080]

Watt had a younger brother, John, who was subsequently lost by shipwreck, in a voyage from Scotland to the United States. This lad, having determined on following the business of his father, left James more completely at liberty to choose his own occupation. But such a choice was difficult for a student who commanded equal success in every thing to which he directed his attention.

The excursions which he was in the habit of making on the Scottish mountains surrounding Loch Lomond, naturally directed his attention to botany and mineralogy, in each of which he attained considerable knowledge. His love of anecdote and romance was likewise gratified by the scenery which he enjoyed in these walks; and the traditions and popular songs with which they made him acquainted. When from ill-health, as constantly happened, he was confined to the house, he devoted himself to chemistry, natural philosophy, and even to medicine and surgery. In chemistry he acquired some experimental skill, and studied with eager zeal the elements of natural philosophy by S'. Gravesande. His own unhappy maladies prompted him to read works on surgery and medicine; and to such an extent did the activity of his mind impel him on these subjects, that he was found one day dissecting, in his room, the head of a child, who had died of some unknown disease, with a view to ascertain the cause of its death.

In 1775, at the age of nineteen, at the recommendation of Dr. Dick, professor of natural philosophy in the university of Glasgow, he went to London, where he employed himself in the house of Mr. John Morgan, a mathematical instrument maker, in Finch Lane, Cornhill, to whom he apprenticed himself for three years. He remained, however, only a year, at the expiration of which (probably owing to his delicate state of health) he was released from his apprenticeship, and returned to Glasgow, with the intention of establishing himself in business as an optician and mathematical instrument maker. In the fulfilment of this intention, however, he was obstructed by the interposition of the Corporation of Trades in that town, who regarded him as an intruder, not qualified by the necessary apprenticeship to carry on business. All means of conciliation being[Pg081]exhausted, the Professors of the University interfered, and gave him the use of three apartments within the college, for carrying on his business, and likewise appointed him mathematical instrument maker to the University. Soon afterwards the opposition of the local trades seems to have given way, and he opened a shop in Glasgow for the sale of mathematical instruments.

After the celebrity at which he has arrived, it will be easily believed that every trace of his earlier connection with Glasgow college is carefully cherished. There are accordingly preserved at that place little instruments and pieces of apparatus of exquisite workmanship, which were executed entirely by the hand of Watt, at a time when he was not in a condition to command the aid of workmen under him.

At the time of obtaining this appointment in the University, Watt was in his twenty-first year. His natural talents and winning manners were speedily the means of gaining for him the esteem and friendship of all those eminent persons connected at the time with that university whose regard was most valued. Among these the earliest of his friends and patrons were—Adam Smith, the author of "The Wealth of Nations;"Black, afterwards celebrated for his chemical discoveries, and more especially for his theory of latent heat; andRobert Simson, rendered illustrious by his works on ancient geometry. In releasing Watt from the persecution of the Glasgow corporation, these distinguished persons first imagined that they were conferring a benefit merely on an industrious and clever artisan, whose engaging manners won their regard; but a short acquaintance with him was sufficient to convince them how superior his mind was to his position, and they conceived towards him the most lively friendship. His shop became the common rendezvous, the afternoon lounge, of all who were most distinguished for literary and scientific attainments among the professors and students. There they met to discuss the topics of the day in art, science, and literature. Among these students, the name which afterwards attained the highest distinctions, and among these distinctions, not the least, the lasting personal friendship and esteem of Watt himself, wasRobison,[Pg082]the author of a well known work on Mechanics, and one of the contributors to theEncyclopœdia Britannica.

The following extract from an unpublished manuscript by Robison himself will show at once the estimation in which Watt was held, and will illustrate one of the most interesting traits of his personal character:—

"I had always, from my earliest youth, a great relish for the natural sciences, and particularly for mathematical and mechanical philosophy, when I was introduced by Drs. Simson, Dick, and Moor, gentlemen eminent for their mathematical abilities, to Mr. Watt. I saw a workman, and expected no more; but was surprised to find a philosopher as young as myself, and always ready to instruct me. I had the vanity to think myself a pretty good proficient in my favourite study, and was rather mortified at finding Mr. Watt so much my superior.. .. Whenever any puzzle came in the way of any of the young students, we went to Mr. Watt. He needed only to be prompted, for every thing became to him the beginning of a new and serious study, and we knew that he would not quit it till he had either discovered its insignificancy, or had made something of it. He learnt the German language in order to peruse Leupold's 'Theatrum Machinarum;' so did I, to know what he was about. Similar reasons made us both learn the Italian language.* * *When to his superiority of knowledge is added thenaïvesimplicity and candour of Mr. Watt's character, it is no wonder that the attachment of his acquaintances was strong. I have seen something of the world, and am obliged to say I never saw such another instance of general and cordial attachment to a person whom all acknowledged to be their superior. But that superiority was concealed under the most amiable candour, and a liberal allowance of merit to every man. Mr. Watt was the first to ascribe to the ingenuity of a friend things which were nothing but his own surmises, followed out and embodied by another. I am the more entitled to say this, as I have often experienced it in my own case."

Watt never permitted the inquiries which arose out of these reunions to interfere with the discharge of the duties of his workshop. There he passed the day, devoting the[Pg083]night to study. Every inquiry appeared to him to be attractive in proportion to its difficulty, and to have charms in proportion as it was removed from the common routine of his business. As an example of this may be mentioned the fact, that, being himself so insensible to the charms of music that he could not distinguish one note from another, he was actually induced to undertake the construction of an organ, in which he was nevertheless completely successful. The instrument he constructed, as might have been expected, contained many improvements in its mechanism; but what is much more remarkable, its tone and its musical qualities commanded the admiration of all the professional musicians who heard it. In the construction of this instrument Watt showed that vigorous spirit of investigation which characterised all the subsequent labours of his life. He made out the scale of temperament by the aid of the phenomena of beats, of which he could only obtain a knowledge by a profound but obscure work published by Dr. Robert Smith of Cambridge.

The earliest occasion on which the attention of Watt is said to have been called to the agency of steam, was in the year 1759, when his friend Robison entertained some speculations for applying that agent as a means of propelling wheel carriages; and he consulted Watt on the subject. No record, however, has been preserved of any experiments which were tried on this occasion; nor does it appear that the inquiry was carried farther than a verbal discussion, such as habitually took place on other subjects of science between Watt and his friends.

(46.)In 1762, Watt tried some experiments on the force of steam at a high pressure, confined in a close digester; and he then constructed a small model to show how motion could be obtained from that power. The practicability of what has since been called theHigh Pressure Engine, was demonstrated by him on this occasion; but he did not pursue the inquiry, on account of the supposed danger of working with such compressed steam as was required.

It is usual to provide, in the cabinets of experimental apparatus for the instruction of the students of universities,[Pg084]small working models of the most useful machines. In the collection for the illustration of the lectures delivered to the Natural Philosophy class in the University of Glasgow was a working model of Newcomen's atmospheric engine, applied to a pump for raising water; which, however, had never been found to work satisfactorily. The Professor of Experimental Philosophy of that day, Dr. John Anderson (the founder of the celebrated Andersonian Institution), sent this model in 1763 to Watt's workshop, to be repaired. Its defects soon disappeared, and it was made to work to the satisfaction of the professor and students.

This simple discharge of his duty, however, did not satisfy the artisan; and his wonted activity of mind rendered this model a subject of profound meditation, and led him into a course of practical inquiry respecting it, which formed the commencement of a most brilliant career of mechanical discovery. The improvement—we might almost say the creation—of the steam engine, by this great man, must not therefore be regarded, as so often happens with mechanical discoveries, as the result of fortuitous observation, or even of a felicitous momentary inspiration. Watt, on the other hand, conducted his investigation by a course of deep thought, and of experiments marked by the last refinement of delicacy and address. If he had received a more extended and liberal education, one would have thought that he had adopted for his guide the celebrated maxim of Bacon:—

"To write, speak, meditate, or act, when we are not provided withfactsto direct our thoughts, is to navigate a coast full of dangers without a pilot, and to launch into the immensity of the ocean without either rudder or compass."

The model which he had repaired, had a cylinder of only two inches diameter, and six inches stroke. After he had put it in complete order, he found, that although the boiler was much larger in proportion to the cylinder than those of real engines, yet, that it was incapable of supplying the cylinder with steam in sufficient quantity to keep it at work. To enable it to continue to move, he found it necessary to lessen the quantity of water raised by its pump, so as to[Pg085]reduce the load on its piston very much below the proper standard according to the common rules for large engines.

He ascribed the great inferiority in the performance of the model, compared with the performance of the large engines, to the small size of the cylinder, and to its material. The cylinder of the model was brass, while those of large engines were of cast iron; and brass being a better conductor of heat than iron, he concluded that more heat in proportion was lost from this cause in the model, than in the larger engines. He observed that the small cylinder was so heated when the steam was admitted into it, that it could not be touched by the hand; but, nevertheless, that this heat contributed nothing to its performance, inasmuch as before the piston descended, the cylinder required to be cooled.

(47.)His first attempt to improve the engine, was by using a wooden cylinder instead of an iron one. He accordingly made a model with a cylinder of wood, soaked in linseed oil, and baked to dryness. With this he made numerous experiments, and found that it required a less quantity of water to be thrown into the cylinder to condense the steam, and that it was worked with a less supply of steam from the boiler than was necessary with the metallic cylinder.

Still he found that the force with which the piston descended was considerably less than that which the atmospheric pressure ought to supply, supposing a tolerably perfect vacuum to be produced under the piston. This led him to suspect that the water injected into the cylinder was not perfectly effectual in condensing the steam. The experiments which he had previously made on the increased temperature at which water boils under pressures greater than that of the atmosphere, led him by analogy to the conclusion that it would boil at lower temperatures if it were submitted to a pressure less than the atmosphere, and he was aware that Dr. Cullen and others had then recently discovered that in vacuo, water would boil at so low a temperature as 100°. These notions suggested the probability that the water injected into the cylinder being heated by the condensed steam, might produce vapour of a low temperature[Pg086]and reduced pressure under the piston, which would account for the deficiency he observed in the power of the engine.

No means occurred to him by which he could ascertain, by direct experiment, the temperatures at which water would boil under pressures less than that of the atmosphere. He sought, however, to determine it by the following method. Having ascertained, by repeating and multiplying the experiments which he had tried in 1762, on high-pressure steam, he obtained a table of the temperatures at which water boils at various pressures greater than that of the atmosphere. These results he laid down in a series forming a curve, of which the abscissa represented the temperatures, and the ordinates the pressures. He then continued this curve, backwards as it were, and obtained, by analogy, an approximation to the boiling temperatures, corresponding to pressures less than that of the atmosphere. In other words, having obtained by his experiments a notion, however imperfect, of the law or rule observed by the temperatures at which water boils at different pressuresgreaterthan that of the atmosphere, he calculated by the same law or rule what the pressures would be at different pressureslessthan that of the atmosphere.

Applying these results to the interior of the cylinder of the atmospheric engine, he obtained an approximation to the pressure of the vapour which would be produced from the warm water formed by the cold water injected into the cylinder, and the steam condensed by it; and he accordingly found that vapour, having a pressure seriously injurious to the power of the engine would be produced in the cylinder, unless considerably more water of injection was thrown in than was customary.

It was apparent that the actual quantity of steam usefully employed in the cylinder at each stroke, was only the quantity which filled the cylinder; and therefore, in order to ascertain the quantity of steam lost by the imperfections of the machine, it was necessary to compare the actual quantity of steam transmitted by the boiler to the cylinder at each stroke, with the quantity which would just fill the cylinder. The difference would of course be wasted. But to determine[Pg087]the actual quantity of steam supplied by the boiler to the cylinder, there was no other means than by observing the quantity of water evaporated in the boiler. That being observed, it was necessary to know the quantity of steam which that water formed; and it was therefore necessary to determine the quantity or volume of steam which a given volume of water produced.

Back to Index Next