sation from the water lying on the top of the piston, as well as from water escaping past it, was very considerable; while, at the same time, the piston rarely travelled a sufficient distance in the cylinder; and a great deal of steam was lost every stroke by filling a useless vacuity. The boilers, besides being too small, were generally badly set, the bottom being too far from the fire; and the firing was badly conducted, the coals being piled in a heap on the middle of the grate, instead of being spread evenly over it. The injection-cistern was generally set too low, by which means the water was not adequately dispersed within the cylinder; and the valve-gearing was for the most part so constructed that the regulator did not open fully, by which means the steam was throttled, and a heavy counter-weight was necessary to suck the steam into the cylinder, which of course had afterwards to be raised at an expenditure of power." The correction of these faults was left for Mr. Smeaton to effect.

Such as we now leave it, was the degree of perfection to which the steam-engine had arrived. The principles of its action apparently precluded the attainment of a higher degree of practical usefulness; and it remained for a brighter genius and a more original mind, than was possessed by any of those who had hitherto directed their attention to the subject, to thoroughly grapple with, and to understand, its defects; and by opening up a new path of discovery, to place the steam-engine, as a social power of rare value, in the high position to which its wonder-working powers has fairly entitled it.

CHAPTER II.

THE HISTORY OF THE INTRODUCTION OF THE MODERN STEAM

ENGINE.

In the year 1736, at the little town of Greenock on the banks of the Clyde, James Watt was born. Of a slender form, sickly appearance, retiring and bashful in his manners, and bearing with him no evidence of an intellectual capacity superior to his fellows, this youth, unaided by family wealth or station, or even by the adventitious aids of an early liberal education, was destined, during a long and active life, to be the means of introducing a power which aided this country materially during a time of difficulty and danger, and to leave behind him a name world-wide in its reputation.

When about sixteen years of age, he became acquainted with an obscure mechanic in Glasgow, who, "by turns a cutler and whitesmith, a repairer of fiddles and a tuner of 'spinnets,' was a useful man at almost every thing;" adding to this list of accomplishments "a knowledge of the construction of mathematical instruments and of 'spectacle-glasses,' he was dignified by the title of 'optician.'" To this individual Watt in his sixteenth year was apprenticed, chiefly, as is probable, more from the fact that it offered an easy calling suitable for his delicate health, than from any inducement it held out as that by which he could afterwards make a fair livelihood. After a short apprenticeship of less than two years, James Watt removed to London, where he succeeded in obtaining employment under a regular mathematical-instrument maker. Here he obtained that knowledge of business habits and processes which had been withheld from him in his earlier engagement. His stay in London was very limited; and probably from a severe cold which he caught while following his avocations, and the effects of which he felt for many years afterwards, he returned to his native town after an absence of little more than a year. He next endeavoured to raise a business of his own, and began to practise both in Greenock and Glasgow. In the latter place he met with an obstacle which threatened to put a sudden stop to his progress; this arose from the fact that he was not a freeman," or " burgess," of the town. spot, however, existed, within the boundaries of which all such absurd laws and regulations were inoperative and harmless for evil;-this was the "College of Glasgow." By the kind offices of some of the dignitaries, Watt was appointed mathematical-instrument maker to the university; and a 100m was allotted him within its precincts, in which he could carry on his avocations without molestation. Thus was the apparently untoward circumstance amply compensated for. And it is by no means idle to conjecture what would have been the results on the future progress of the

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steam-engine had that absurd law not been in existence which drove Watt out of what might be looked upon as the open path of commerce, to take refuge in the place, of all others, the best fitted for, and offering the most eligible opportunities of, carrying on the series of experiments which by a fortuitous chain of circumstances were shortly presented to his notice; and by the successful prosecution of which he was destined to make himself so famous.

In the year 1759, in this situation, Watt had his attention directed to the subject of the steam-engine through the representation of Mr. Robinson, afterwards Professor of Natural Philosophy in the University of Edinburgh, and author of the well-known work entitled Elements of Mechanical Philosophy. The scheme proposed had reference to the moving of wheelcarriages by the aid of steam; but in consequence of Mr. Robinson leaving college, it was abandoned. Two years afterwards, however, Watt again returned to the subject, and instituted some experiments with a Papin's digester; and formed a sort of steam-engine "by fixing upon it a syringe one-third of an inch in diameter, and furnished," says Mr. Watt, whose own account we now quote, "also with a cock to admit the steam from the digester or shut it off at pleasure, as well as to open a communication from the inside of the syringe to the open air, by which the steam contained in the syringe might escape. When the communication between the cylinder and digester was opened, the steam entered the syringe; and by its action upon the piston, raised a considerable weight (15 lbs.), with which it was loaded. When this was raised as high as was thought proper, the communication with the digester was shut off, and that with the atmosphere opened; the steam then made its escape, and the weight descended. The operations were repeated; and though in this experiment the cock was turned by hand, it was easy to see how it could be done by the machine itself, and make it work with perfect regularity. But I soon relinquished the idea of constructing an engine upon this principle, from being sensible it would be liable to some of the objections against Savery's engine, namely, from the danger of bursting the boiler, and the difficulty of making the joints tight; and also that a great part of the power of the steam would be lost, because no vacuum was formed to assist the descent of the piston."

Two years after relinquishing his experiment, as above stated, his attention was again directed to the subject, by a model of a steam-engine on Newcomen's plan, belonging to the Natural Philosophy class, being placed in his hands to be repaired (1763-4). At first directing his attention to the dry matter-of-fact details of the task he had intrusted to him, his active mind received a new impulse from the result of one or two trials of the engine, and he directed the full energy of his intellect to master the principle of the machine, and to ascertain the cause of its defects as an economical prime-mover. In conducting the experiments, two things attracted his attention; the first was the great loss of steam from the condensation caused by the cold surface of the cylinder; secondly, the great quantity of heat contained in a small quantity of water when converted into steam. If a quantity of water is heated in a close boiler some degrees above the boiling-point, and the steam suffered to escape suddenly, the temperature of the boiling-water remaining in the boiler will be reduced to the ordinary boiling-point. The steam, however, which escaped, although carrying off all the excess of heat, would, if condensed, form but a small quantity of water. The saving of this heat

was therefore a matter of the highest importance. The loss of steam occasioned by the alternate heating and cooling of the cylinder was sufficient to fill the cylinder three or four times, and to work the engine. "By means of a glass tube inserted into the spout of a tea-kettle, he allowed the steam to flow into a glass of cold-water until it was boiling hot. The water was then found to have gained nearly a sixth part by the steam which had been condensed to heat it, and he drew the conclusion that a measure of water converted into steam can raise about six measures of water to its own heat, or eighteen hundred measures of steam can heat six measures of water." "Hence he saw that six times the difference of temperature, or fully 100 degrees of heat, had been employed in giving elasticity to steam, and which must all be subtracted before a complete vacuum could be obtained under the piston of a steam-engine." Being struck," says Mr. Watt, "with this remarkable fact, and not understanding the reason of it, I mentioned it to my friend Dr. Black, who then explained to me his doctrine of latent heat, which he had taught some time before this period (summer of 1764); but having been occupied with the pursuits of business, if I had heard of it I had not attended to it, when I thus stumbled upon one of the material facts by which that beautiful theory is supported." In making his experiments, Watt found that the boiler of the model, although large enough according to the standard then in use, did not supply steam fast enough for the wants of the engine, which had a cylinder two inches diameter and six inches stroke. The vacuum too was very imperfect, yet required a large quantity of injection-water to effect it. These defects he attributed to the fact that a small cylinder consumed a greater quantity of steam than a larger one, in consequence of the condensation caused by the increased surface in proportion to its capacity. This defect he sought to remedy by substituting a cylinder made of materials which would conduct heat more slowly than brass, of which the model cylinder was made. For this purpose he constructed one of wood soaked in linseed-oil, and baked dry. This, however, was a failure, for in addition to its want of durability, an essential feature in practice, it was found to condense the steam as much as before. The principal loss sustained was, therefore, by the alternate heating and cooling of the cylinder; and the conviction was forced upon him that the grand secret lay in being able to effect the condensation of the steam without cooling the cylinder. To the attainment of this Watt directed his whole energies, and in the year 1765 the felicitous idea struck him, "that if a communication were opened between a cylinder containing steam, and another vessel were exhausted of air and other fluids, the steam, as an expansible fluid, would immediately rush into the empty vessel, and continue to do so until it had established an equilibrium; and if that vessel were kept very cool by an injection or otherwise, more steam would continue to enter until the whole was condensed." This brilliant idea was soon put to the test of experiment and found correct; and thus was solved the great problem which had for so many years perplexed and baffled his predecessors. It is said, that as soon as this happy thought had been realised, all the train of details necessary to carry it into efficient practice followed in rapid succession; and that not for a moment had he any hesitation in conceiving the rapid and immediate perfecting of the whole machine. In carrying out the idea into practice, the first difficulty that presented itself to the mind of Watt was, doubtless, a means of reliev

ing the condenser from the accumulated water which would result from the successive condensation effected in it. This might, of course, be drawn away by the simple force of gravity, by using a pipe thirty feet long, as in Newcomen's engine. This plan, however, would not be effectual for removing the uncondensed steam, or the air that might find its way into the condenser. Some other plan was therefore desiderated. Watt proposed and adopted a pump which would draw off the contents of the condenser, this pump being worked by the engine itself. This constituted another step towards the perfecting of the mechanism: others rapidly followed. The next improvement was surrounding the cylinder with a casing, by which the heat would be retained. This of itself, however, would not effect the desired end: he therefore, to prevent the action of the cold atmosphere on the upper surface of the piston and on the interior surface of the cylinder, which would necessarily be exposed on its descent, closed the top of the cylinder with a close-fitting cover, in the centre of which the piston-rod worked through an aperture rendered tight by what is termed a stuffingbox." The necessity of adopting the next expedient suggested to him was thus made obvious; and in place of the power of the atmosphere he employed the " elasticity of the steam from the boiler to impel the piston down the cylinder." By this arrangement the method adopted of keeping the piston tight, by having water on its upper surface, was precluded from use; and instead, Watt adopted a hemp-packed piston lubricated with tallow. Thus, by successive improvements, the atmospheric engine was changed into a "steam-engine."

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Before illustrating the improvements introduced by Watt, we propose to trace further the points connected with its history. Although the claim of Watt to the originality of the idea of separate condensation is now generally, if not universally, acknowledged, still it is but right to notice that of another party to this high honour. The claim is put forward by Mr. Hornblower, a rival and contemporary of Watt, in Gregory's Mechanics (vol. ii. first edition, p. 362), in the following statement: "About the time that Mr. Watt was engaged in bringing forward the improvement of the engine, it occurred to Mr. Gainsborough, the pastor of a dissenting congregation at Henley-upon-Thames, and brother to the painter of that name, that it would be a great improvement to condense the steam in a vessel distinct from the cylinder where the vacuum was formed; and he undertook a set of experiments to apply the principle he had established; which he did by placing a small vessel by the side of the cylinder, which was to receive just so much steam from the boiler as would discharge the air and condensing water, in the same manner as was the practice from the cylinder itself in the Newcomenian method, that is, by the snifting-valve and sinking-pipe. In this manner he used no more steam than was just necessary for that particular purpose, which, at the instant of discharging, was entirely uncommunicated with the main cylinder, so that the cylinder was kept constantly as hot as the steam could make it. Whether he closed the cylinder, as Mr. Watt does, is uncertain; but his model succeeded so well as to induce some of the Cornish adventurers to send their engineers to examine it; and their report was so favourable as to induce an intention of adopting it. This, however, was soon after Mr. Watt had his act of parliament passed for the extension of his term; and he had about the same time made proposals to the Cornish gentlemen to send his engine into

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