Mr. Stephenson also improved the working of the "Rocket" engine, and, by applying the steam more powerfully in the chimney, to increase the draught, was enabled to raise a much greater quantity of steam than before. The following is the result of an experiment made with this engine, in dragging heavy loads:

equal to 13 miles per hour, nearly, with an average load of 40 tons.

No account was kept of the quantity of fuel consumed, but, as there was a lock-up valve, the steam could not be raised higher than 50 lbs. per square inch.

The following Experiments were likewise made by Mr. Stephenson, upon the same piece of road.

EXPERIMENT III.

Phoenix engine, having ninety tubes, each two inches. in diameter; area of grate-bars, six square feet; extent of radiant, twenty square feet; and of surfaces exposed to the heated air and flame, 138.8 square feet.

34 tons, conveyed over a space of 43 miles, with a consumption of 1422 lbs. of coke. The average speed being from ten to twelve miles per hour. This is equal to 1500 tons, conveyed one mile. Consumption of fuel, including the engine and tender (seven tons), 0-78 lbs. per ton, per mile; exclusive of the engine, 0.94 lbs. per ton, per mile; and taking the goods, equal

to two thirds of the gross weight, 1.42 lbs. per ton, per mile.

EXPERIMENT IV.

"Arrow" engine, of similar construction to the last, with ninety-two tubes, each two inches in diameter, passing through the boiler; area of fire-grate, six square feet; extent of radiant surface, twenty square feet; and extent of communicative surface, 144.81 square feet.

28 tons, conveyed over a space of 36 miles, and 321 tons, conveyed six miles, equal to 1208 tons, conveyed one mile; consumption of coke, 1008 lbs. The average speed being twelve miles an hour. The consumption of fuel in this Experiment will, therefore, be, including the weight of the engine and tender, 0·67 lbs. per ton, per mile; or, exclusive of the engine and tender, 0.83 lbs. per ton, per mile; and for useful weight, or goods, 1.25 lbs. per ton, per mile.

The following Table will shew the result of the foregoing Experiments, on the consumption of fuel, and performance of these engines.

We see, from the above table, in a very striking point of view, the effect of employing engines of light weights, and small power, in the conveyance of goods, when travelling at great rates of speed. Although the "Rocket" engine consumed only 117 lbs. of coke in the evaporation of each cubic foot of water, while the old engines required 18.34 lbs.; or, in point of fact, although the steam in the "Rocket" engine was more economically generated, in the proportion of 11: 18; yet, by that engine, when travelling at a quick rate of speed, only taking three times its weight of carriages, the expense of fuel per ton per mile is greater than in old engines. The great improvement is, however, in the evaporating powers, which is shewn, by the above table, to be increased from 15.92 cubic feet an hour by the old engines, to forty-four cubic feet per hour by the Arrow engine.

Following up these improvements, shortly after the experiments were made, two engines of large dimensions were put upon the Liverpool and Manchester railroads, and the following account of their performance was published at the time. The Sampson engine, weighing eight tons, with the front and hind wheels of the same diameter, proceeded from Liverpool to Manchester with a gross load of 153 tons 11 cwt., and being assisted up the inclined plane by the Goliah engine, reached to the latter place about eleven o'clock; the consumption of coke in this journey was only one third of a pound per ton per mile gross, or about one half of a pound per ton per mile of goods.

Since that period these engines have been still further improved, and improvements are at present going on, which will no doubt increase their power much beyond what they are at present; it will, therefore, be difficult to assign any specific amount of power, or fixed per

formance of this kind of engine, except in terms of the power of raising steam. We shall, therefore, first of all, ascertain the evaporating powers of the best of the engines at present in use, and, from the observed performances of these engines, endeavour to determine upon the power of other engines, according to their powers of raising steam.

Art. 6.-Evaporating Powers of Locomotive

Engines.

Before giving the experiments made on the relative evaporating powers of the different engines, however, it will be necessary to offer one or two explanations of the manner in which the steam is produced in those engines.

The evaporation of steam is accomplished by two distinct modes, the direct action of the fire upon that part of the boiler which encloses it, and which is called the radiant heat; and the action of the heated air, passing from the fire through the tubes, which is called the communicative heat. All the water, therefore, which surrounds the fire-box, enveloping the fire, and the water against that end of the boiler, is exposed to the radiant heat of the fire; while the water which surrounds the tubes, is only exposed to the communicative heat, given out from the heated air in its passage from the fire to the chimney.

In the old engines the fire was placed within a tube, which either passed directly through the boiler from the fire to the chimney, or which passed from the fire to nearly the opposite end of the boiler, returned, and passed out to the chimney, at the same end of the boiler as that in which the fire was placed. The experiments previously detailed shew the evaporating

powers of several of the old engines, the greatest of which does not appear to exceed sixteen cubic feet of water an hour, with engines having the fire within the boiler, and weighing about six tons.

Hackworth's engine, which was of this description, at the Liverpool contest, evaporated about twenty-four cubic feet per hour; but this, as previously explained, was accomplished at the expense of an increase in the consumption of fuel above that of the old engines in the proportion of 28.8 to 18.34 lbs. of coke for every cubic foot of water evaporated. We cannot, therefore, take the evaporating powers of engines with the fire within the boiler, and where the heated air passes through a single tube, at more than sixteen cubic feet of water per hour.

a.—Evaporating Power of the Killingworth improved Engine.

In the description of the different kinds of engines we have given an account of one, used on the Killingworth railway, with the fire placed within the boiler, and in which the heated air passes, through several small tubes, from the fire into the chimney. In an experiment made with this engine, of the following dimensions,— boiler, nine feet two inches long, four feet in diameter; elliptical tube, within which the fire is placed, two feet four inches broad by two feet in height, and four feet eight inches long; area of fire-grate, 12.9 square feet; number of tubes, forty-three, each four feet and a half long, and two inches in diameter; area of radiant surface, 22.56 square feet; area of communicative surface, 101.5 square feet; volume of heated air, passing through the tubes, 135 square inches; load, sixty tons, exclusive of tender; - the velocity upon a level railroad