IXX

THE great practice Smeaton had in planning machinery on a grand scale, was amply merited by the pains he took to become master of the knowledge of every circumstance which could affect its action or power. After his judgment had become matured by experience, he placed little if any dependence on theory; but became a diligent collector of facts regarding the peculiarities, proportions, and effect of machines which had been erected by others. This gave a consistency and precision to his opinions and practice, that we look for in vain in the works of his cotemporaries; they do not appear to have felt that the routine of their practice might be corrected, by observing even the mistakes of others, or they were too idle to look beyond their own Gotham for improvement.

It is on account of this well-directed industry, that his labours are yet esteemed as standards of construction, and of well understood and effective

292

ENGINES AT NEWCASTLE.

combination. And the most flattering testimony that could have been borne to the success of his deviation from the beaten tract to improve the steam-engine, is furnished by Watt. When speaking to him about the terms upon which he granted permission to use the condensing engine, "We charge," says he, "our profits, in proportion to the saving of fuel made in our engines, when compared with a common one, which burns the same kind of coals. We ask a third part of these savings, but in all these comparisons, our own interest makes us except your improved engines, unless we were allowed a greater proportion of the savings."

The value of these improvements will be best understood from experiments he made in 1769. At that period fifty-seven engines were in operation at Newcastle, having a total area of piston, equal to 116,435 square inches, and operating with a power equal to that which could be exerted by 1,188 horses.

Fifteen of these machines were selected, as being a fair specimen in every case of the whole number, having an energy equal to that of 376.5 horses. The total superficial area of their pistons was 36,899 square inches, having an average pressure of 6.72 pounds on each inch of piston, which moved at a speed of 100 2 feet per minute, and raised a weight of 5'6 millions of pounds to a height of one foot, with eighty-four pounds weight of Newcastle coal.

So small an effect, with so great an expenditure of fuel, appeared to Smeaton to arise from incorrect proportions given to the various parts of which the mechanism was composed. The boilers, he imagined, were too small to generate the proper quantity of steam, and this defect was aggravated

DEFECTS OF THESE.

293

by an improper formation of their fire-places. The management of the fire too was little understood, and carelessly attended to. The pipe conducting the steam to the cylinder, had not sufficient capacity to allow it to flow into the cylinder with the proper velocity. The injection cistern was placed too low; the water laying on the piston, abstracted the heat from an immense quantity of vapour. The cylinder itself was faulty in proportion, and very defective in its execution. Every thing appeared as if it had been placed in its position by chance, and proportioned in the same manner; but as often as one machine was found better than another in one part, this was neutralized by its more glaring faults in another part, so that with so great a latitude, no one had had the good fortune for his guessings to have been the right one.

Yet, although the greater number of these defects were so obvious, and of such magnitude, that the removal of even one of them would have added greatly to the power of the apparatus, they were totally overlooked by the fabricators of the mechanism. If they found a deficiency of power, they increased the area of the piston, estimating the effect by the weight placed upon it, without reference to the velocity with which it moved, or to the quantity of coal which was consumed to produce it.

Smeaton soon found that the attempt to get the information he desired, from trials upon engines in operation, was beset with very great difficulties; no estate could have survived the expense of making a series of experiments, where each would absorb a moderate fortune. He took the next best plan, and erected a small engine at his house at Austhorpe ; with this during four years he made a great number of experiments, on every point

294

SMEATON'S IMPROVEMENTS.

which he thought might affect the action of the atmospheric engine By mere attention to keeping a thin clear fire evenly spread over the grate, he saved a sixth part of the heat with a more regular performance. An increase of effect was also produced by admitting air under the piston during the returning stroke, or when the counterweight was drawing up the piston. He minutely examined the action and effect of the injection, and found that, by apportioning it, he could regulate the motion of the piston; he saw that there was a loss of power from regulating the motion of the engine by a cataract. He also ascertained the quantity of water evaporated by a given weight of fuel; he defined the best proportion of the surface of boiler, that should be submitted to the action of the fire to generate a given quantity of vapour. He pointed out the proportion of vapour that was condensed in merely heating the cylinder and piston, without producing any useful effect besides that, and overcoming friction, and the best velocity with which the piston should move, and the load it should carry. He made some minor improvements in the material of which the under side of the piston was formed, the construction of the jet orifice, the framing of the great lever, the arrangement and construction of the hand-gear, and in the framing and proportions of the parts throughout.

The first opportunity he had of carrying his ideas into practice, was at a coal mine near Newcastle. The engine he was called upon to improve, had a cylinder fifty-two inches in diameter, which, when loaded with 8.92 pounds on each square inch, and moving at the rate of 54.25 feet each minute, raised 4 82 millions of pounds' weight one foot high, with an expenditure of eighty-four pounds' weight of Newcastle coal.

SMEATON'S ENGINE.

295

In the new arrangement, Smeaton retained the old cylinder and pump-work; he made the piston move through eighty-four feet in a minute, with a weight of 7-5 pounds on each inch, and he thus raised 9.45 millions of pounds one foot high, by the same weight of coals which could only raise about half the weight in the machine which had been superseded. This increase of effect was independent of friction and other resistances; but as there was a weight of upwards of twenty-seven tons poised on the axis of the lever during the falling of the piston, and about 92 tons during its returning stroke, taking the loss of effect from moving this enormous weight into account, the eighty-four pounds of coal may be estimated to have raised eleven millions of pounds one foot high, and that too with a much greater uniformity of action than was produced in the old engine.

The general form of the details of the engines which were designed by Smeaton, is shown in the engraving. The engine for which these were constructed was erected at the Chacewater mine, in Cornwall, and was accounted at the time one of the most powerful machines which had been used in England. Its cylinder was 72 inches in diameter; the piston had a 94 feet stroke; the water was drawn at three lifts from a depth of 50 fathoms, and the weight of it in the pumps was upwards of 14 tons. The working beam was 6 feet 2 inches in depth, and composed of 20 fir beams, united together by massive hoops of iron. Three boilers were attached to this huge apparatus; one of these was placed as shown in the engraving, the other two were placed in the outside of the engine house, each in its separate building.