We shall, in the first place, give a brief sketch of the construction of the different engines, and then offer a few remarks on the important improvements, to which these experiments have led.

Art. 11.-Description of the "Rocket" Engine.

The "Rocket" engine, of Mr. R. Stephenson, shewn in the engraving, No. 7, opposite, differs from the locomotive engines previously described in this work, in the mode of raising steam. The boiler, a, is cylindrical, with flat ends, six feet long, and three feet four inches diameter. To one end of the boiler is attached a square box, or furnace, в, three feet long, by two feet broad, and about three feet deep; at the bottom of this box, the fire-bars, F, are placed, and it is entirely surrounded by a casing, except at the bottom, and on the side next the boiler, leaving a space of about three inches between this casing and the furnace, which space is kept constantly filled with water; a pipe, c, on the under side, communicating with the boiler, supplies it with water; and another pipe, D, at the top, allows the steam to pass off into the boiler. upper half of the boiler is used as a reservoir for steam, the lower half being kept filled with water. Through the latter part of the boiler, copper tubes reach from one end of the boiler to the other, shewn in No. 8, being open to the fire-box, at one end, and to the chimney at the other. In the boiler of the "Rocket," there were twenty-five tubes, three inches in diameter. The cylinders were placed, one on each side of the boiler, as shewn in the drawing, and worked one pair of wheels only; were eight inches diameter, with a stroke of sixteen inches and a half; diameter of large wheels, four feet eight inches and a half. A slight inspection of the

The

No. 8.

No. 7.

drawing will shew that the principle of generating steam by this engine, is the exhausting power of the chimney, which is aided by the impulse of the steam

from the cylinders, being thrown into the chimney by two pipes, E, one from each of the cylinders. The area of surface of water, exposed to the radiant heat of the fire, was twenty square feet, being that surround

ing the fire-box or furnace; and the surface exposed to the heated air or flame from the furnace, or what we shall call communicative heat, 117.8 square feet; the area of the grate-bars being six square feet. The end view, No. 8, will shew the disposition of the tubes in the end of the boiler, with the fire-box surrounding the end.

Art. 12.-Description of the "Sans Pareil" Engine. The Sans Pareil," of Mr. Hackworth, is of the same principle as the "Rocket;" the combustion of the fuel being effected by the exhausting power of the chimney, and the ejection of the steam from the cylinders into the chimney.

No. 9.

The accompanying sketch, No. 9, will shew the form of boiler, which is cylindrical, four feet two inches in diameter, with one flat, and one hemispherical end, and six feet long. The cylinders were placed one on each side of the boiler, and immediately above one of the pairs of wheels; the other two wheels being connected with them by side rods. Cylinders, seven inches; length of stroke, eighteen inches; diameter of wheels, four feet and a half.

The steam is generated by means of a double tube, as shewn in the sketch, No. 10, passing nearly from one

end of the boiler to the other, and then returning; the fire-grate and chimney being thus both at the same end of the boiler, A, No. 10, shews the grate-bars, bb, the tube, and c, the chimney. The tube projects, from the end of the boiler, about three feet; and at the fire end a semi-circular casing surrounds the top of the tube, to the extent of the whole three feet, but at the chimney end the casing extends only two feet. This was for the double purpose of obtaining an area of heating surface, and to allow sufficient air to pass through the fire-grate, which tubes placed entirely within the boiler do not possess. At the fire end the tube was two feet in diameter, tapering away to fifteen inches, the diameter at the chimney; the length of grate-bars being five

feet. The area of surface of water exposed to the direct action of the fire or radiant heat, was, therefore, 157 square feet; and to the communicative power of the heated air and flame, 74-6 square feet, the area of the fire-grate being ten square feet.

Art. 13.-Description of the " Novelty" Engine.

Messrs. Braithwaite and Erickson's engine, the "Novelty," is of a different principle, the air being driven or forced through the fire by means of a bellows. The accompanying drawings will shew the general construction of this engine, and more particularly the generator, or mode of raising the steam, which constitutes its prominent peculiarity. In the sketch, No. 11, A is the

generator, the lower part of which is filled with water, and the upper part is a chamber for the steam; connected with this is the horizontal generator, B, which being placed below the top of the water in the upright generator, A, is constantly filled with water. A tube, c,