MARINE ENGINES.

THE OSCILLATING ENGINE.

The vibrating or oscillating engine introduced by Maudslay in 1827,with its varied modern improvements, is very suitable for paddle-wheel steamers, the comparatively small space it requires fitting itadmirably for this dass of vessel. It is the most direct-acting kindof engine which we have; the piston rod is connected to the crankpin directly, thus saving height in the engines where that is adesideratum, and the weight is most satisfactorily placed, beingneither too high nor too low in the ship. The many examples—from the small river boats on the Thames of 30 lrorse-power collec-tively, to large ocean steam ships such as the Great Eastern, thelargest ship as yet constructed, with oscillating engines for thepaddle wheels of 1000 nominal horse-power collectively—all beartestimony to the success of the oscillating type of engine. It maybe regarded as the only example left of the many classes of enginesthat have been successfully applied to paddle-wheel ships; andfrom our being able to couple the crosshead of the piston roddirectly on the crank pin, and keep the weight of the machinerybelow the deck, the oscillating engine is likely to remain long in usefor shallow river boats propelled by paddle wheels, for undoubtedlythis method of propulsion possesses many advantages over thescrew propeller for vessels of light draught, especially when theyare built to attain great speed.

The peculiar motion of these engines—the cylinders vibrating oncentral hollow trunnions—requires the parts to be nicely balanced;and as the piston rod takes the side strain and the strains impartedby the action of the steam on the piston, it requires to be made oigreater diameter than for ordinary engines, where it is only sub-jected to tension and compressive stress.

The trunnions should be so placed that the preponderance of theweight of the cylinder is towards the bottom, by which means the