146

MOTIVE POWER AND DISPOSITION

The boiler is of malleable iron, cylindrical with hemis-pherical ends. A cylindrical tube passes through theboiler, within two inches of the bottom; in one endof the tube the fire is put, and the other end is ter-minated by a chimney. The grate, whereon the fire islaid, is placed rather below the middle of the tube, andreaches about four feet within it, resting at the furtherend, upon a narrow partition of brick, closing up the lowerside of the tube below the bars. F, Fig. II. shews the firedoor, which, at the tube end of the fire, closes up the upperside of the tube, thus forcing the air through the fire in theusual manner. The boiler rests upon a square frame ofmalleable iron, supported by the steam cylinders a a,previously described, two on each side, seven inchesdiameter; the cylinders are partly placed within the boiler,as shewn in the drawing, and are nine inches diameter,and lined on the inside with sheet copper; the piston-rodswork through stuffing boxes, in the usual way, and areattached to the cross-beams B B and C C, sometimesformed of one piece, and sometimes of more than one, asrepresented in Fig. II. The rectilinear motion of the piston-rod is secured by the slides s s s s, fastened to the project-ing arms c c, cast upon the top of the cylinder, and keptperpendicular by the braces b b.

The connecting rods D D and C D are fixed upon theends of the cross-beams by ball and socket joints; and,at the other end, by similar joints, to a pin fixed in one ofthe spokes of the engine-wheels, at D D; to strengthenthis spoke, a circhlar piece of metal attaches the twoadjoining spokes with it.

The wheels, as shewn in the drawing, are four feet diame-ter, and are made of cast-iron with circular naves, rimmedout to fit the axle, and fastened to it by means of iron keys.

The axles are of wrought-iron, about three inches and