Engines fitted with the ordinary rigid bearings require to be erected on a firm foundation, and to be kept in perfect line. If, by the settling of the foundation, or from any other cause, they get out of line, heating, cutting, and thumping result. To obviate this, modern engines are often fitted with self-adjusting bearings throughout; this gives the engine great flexibility and freedom from friction. The accompanying cuts show clearly how this is accomplished. The pillow-block has a spherical shell turned and fitted into the spherically-bored pillow-block, thus allowing a slight angular motion in any direction. The connecting-rod is forged in a single piece, without straps, gibs, or key, and is mortised through at each end for the reception of the brass boxes, which are curved on their backs, and fit the cheek-pieces, between which they can turn to adjust themselves to the pins, in the plane of the axis of the rod. The adjustment for wear is made by wedge-blocks and set screws, as shown, and they are so constructed that the parts cannot get loose and cause a break-down. The cross-head has adjustable gibs on each side, turned to fit the slides, which are cast solidly in the frame, and bored out exactly in the line with the cylinder. This permits it freely to turn on its axis, and, in connection with the adjustable boxes in the connecting-rod, allows a perfect self-adjustment to the line of the crank-pin. The out-board bearing may be moved an inch or more out of position in any direction, without detriment to the running of the engine, all bearings accommodating themselves perfectly to whatever position the shaft may assume. The ports and valve-passages are proportioned as in locomotive practice. The valve-seat is adapted to the ordinary plain slide or D-valve, should it be preferred, but the balanced piston slide-valve works with equal ease whether the steam-pressure is 10 or 100 pounds, and at the same time gives double steam and exhaust openings, which greatly facilitates the entrance of the steam to, and its escape from, the cylinder, thus securing a nearer approach to boiler-pressure and a less back-pressure, saving the power required to work an ordinary valve, and reducing the wear of valve-gear. This is a type of engine frequently seen in the United States, but more rarely in Europe. It is an excellent form of engine. The vertical direct-acting engine is sometimes, though rarely, built of very considerable size, and these large engines are more frequently seen in rolling-mills than elsewhere.