STATIONARY ENGINES.

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bedded on a base plate, yet reduces the height of the lever wallconsiderably, while its arrangement is somewhat simpler than in theforegoing example. The valve gear is placed between the cylinderand the main centre of the side levers; thus the additional beamfor working the plug rod is dispensed with, the rod being workeddirectly from a cross gudgeon between the two side levers; thisgudgeon has an elongated hole for the rod to pass through, and isfitted with two side links connected to a crosshead on the plug rod,the rod being guided through bushes at the top and bottom. Allthe other pumps are worked directly from a gudgeon placed betweenthe side levers, and securely keyed to them; but the main pumpgudgeon has a bearing at each end, working on turned bushes onthe under side. This gudgeon is made flat in the body, beingdeeper at the middle, and the pump rods of wood are securelyfastened to it by means of wrought-iron Straps, the great length ofthe pump rods causing them to bend with the versed sine describedby the side levers. The pillow blocks for carrying the side leversare provided with a broad base plate, securely bolted down to thelever wall; the caps for the pillow blocks are simply Shells, fitted forthe sake of appearance, as indeed are all the covers for the pillowblocks of Cornish engines when adapted for mining purposes. Thisarrangement is adopted owing to the steam acting on the top of thepiston at one end of the beam, while the great weight of the pumprods is being lifted at its other end; and in the outgoing stroke, ordescent of the pump rods, the steam pressure on the top of thepiston is in excess of the under side, and consequently the sidelevers have no tendency to lift.

Some mine-pumping engines have been erected on the direct-action principle, the steam cylinder being placed directly over thepumping shaft, with the pump rods attached directly to the pistonrod, the steam acting on the under side of the piston. There is noequilibrium valve fitted to this dass, as the steam, after doing dutyin lifting the pump rods, is exhausted into the condenser, which isin connection with the top of the cylinder, and the downwardmotion of the pump rods is retarded. The weight of these rods isalways in excess of what is required for forcing the water, and isdue to the diameter of the pump and the great length of the rods.Of course the steam in the cylinder can be throttled in its passageto the condenser, thus gradually reducing the pressure and prevent-ing the pump rods descending too rapidly. The air pump is worked