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."

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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that county. This necessarily brought on a competition, in which Mr. Watt succeeded; but it was asserted by Mr. Gainsborough, that the mode of condensing out of the cylinder was communicated to Mr. Watt by the officious folly of an acquaintance, who was fully informed of what Mr. Gainsborough had in hand. This circumstance, as here related, receives some confirmation by a declaration of Mr. Gainsborough, the painter, to Mr. More, late Secretary to the Society for the Encouragement of the Arts, who gave the writer of this article the information; and it is well known that Mr. Gainsborough opposed the petition to parliament through the interest of General Conway." Much doubt is, however, thrown upon the accuracy of this statement, from the fact, that Mr. More, the gentleman alluded to, in a trial, Bolton v. Bull, distinctly stated on oath, that he “ saw the principle laid down in Mr. Watt's specification either applied to the steam-engine previous to his taking it up, or ever read of any such thing whatever." It is not now an easy matter to reconcile this contradiction with the statement of Mr. Hornblower. Having given a brief statement regarding the claim made to the honour of the discovery of separate condensation, we now proceed to note the various steps in the history of the introduction of Watt's steam-engine.

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Having satisfied himself as to the correctness of his principle, Watt proceeded to test it still further by the aid of a model on a large scale. The cylinder of this model was 9 inches diameter, and the piston-rod was attached to a balanced beam. An accident, however, occurred, which, along with his want of means, as well as of time to prosecute his experiments, brought his labours to a close. Having taken up the practice of a land-surveyor and engineer, and his time being pretty fully occupied, the invention lay dormant on his hands for three or four years. His silence on the matter doubtless proceeded from a variety of causes, the principal of which was, likely, the fact, that as a fair trial could only be given to his engine on a large scale, the risk of bringing it out would be too great, the apparatus required being exceedingly costly. From Watt's practice as an engineer, he became acquainted, however, with the celebrated Dr. Roebuck, an enterprising English gentleman resident in Scotland. An able practical chemist, he had succeeded in discovering a method of making sulphuric acid at a comparatively low cost; and being possessed of business habits and qualities of the first order, he succeeded in establishing at Prestonpans, near Edinburgh, a manufactory, in which the process was carried out on a large scale. The profits accruing from this establishment were such, that he gave up the practice of his profession, and confined his attention to carrying out commercial projects on a large scale. He founded the celebrated iron-works at Carron, which, as a project, were highly suc cessful. Urged by his success in this undertaking, he leased the estate of Kinneil, a few miles from Carron, and which contained extensive beds of coal. While carrying on his operations there with the same energy which characterised his other proceedings, he became acquainted with Watt, who, no doubt, struck by his ability and business habits, looked upon him as one in every respect calculated to aid the undertaking of bringing the steam-engine into practice, and accordingly confided to him the secret of his discovery. Dr. Roebuck consented to bear the expense of conducting trials on a large scale; and Watt forthwith proceeded to construct a large engine under his inspection. For a period of eight months, alter

ations and improvements succeeded each other, until at last the engine was brought to a state of comparative perfection-so far, at least, as could be attained, from the imperfect style of workmanship then available. The engine was tried at a coal-mine on Dr. Roebuck's estate; and such was the satisfactory nature of its operations, both as regarded the great saving of fuel and the water used for condensation, that Dr. Roebuck was satisfied as to its powers and capabilities, and closed with Watt, supplying the necessary funds to take out a patent, and to establish a manufactory for the production of the engines; the terms of partnership being, that the money for the above purposes was to be found by Roebuck, he obtaining two-thirds of the profits. On these terms Watt proceeded with his patent, which was taken out in 1769, and of which the following is the specification. It was not accompanied with drawings or sketches of any kind.

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

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

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Secondly: In engines that are to be worked wholly or partially by condensation of steam, the steam is to be condensed in vessels distinct from the steam-vessels or cylinders, although occasionally communicating with them: these vessels I call condensers; and whilst the engines are working, these condensers ought at least to be kept as cold as the air in the neighbourhood of the engines, by application of water or other cold bodies.

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

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

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

"And the said James Watt, by a memorandum added to the said specification, declared, that he did not intend that any thing in the fourth article should be understood to extend to any engine where the water to be raised enters the steam-vessel itself, or any vessel having an open communication with it."

After Watt had obtained his patent, he proceeded to perfect the details of his engine. From the bad workmanship which he had to contend with, his difficulties were of a serious kind; that which harassed him most being the difficulty of keeping the piston tight without incurring a heavy