STATIONARY ENGINES.

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can be lifted and turned in less than two minutes. The plan ofusing an accumuiator charged in this way has been adopted for arailway drawbridge near Caermarthen; and it can be applied tomany other purposes requiring a concentrated exertion of powerwith intervening periods of inaction.

One application of water pressure with an accumuiator, for thepurpose of rapidly lifting or lowering heavy loads, calls for specialnotice because of its growing importance. We refer to verticalhoists at the landing stations of steam ferries, where the traffic of arailway is required to be passed over a river or estuary not spannedby a bridge. The traffic of the Aix-la-Chapelle , Düsseldorf , andRuhrort Railway is by this means shipped and unshipped at theferry across the Rhine ; and such is the rapidity and facility of theOperation that a train of twelve coal Waggons , weighing collectively133 tons, can be transferred from the deck of the steamer to therailway, a height of about 20 feet, in twelve minutes. Each hoistlifts two waggons at a time, and raises its load in ten or twelveseconds. These hoists are so arranged as always to accommodatethemselves to the level of the boat, and also to stop at the exactlevel of the railway.

WATER POWER FROM NATURAL FALLS.

Having said this much on that branch of the subject whichembraces the two principles of accumulation and transmission ofwater power, we will now notice the applications of water pressureas derived from natural falls. When the moving power consists ofa natural column of water, the pressure rarely exceeds 250 or 300feet; and in such cases, to produce rotary motion, a pair of cylin-ders and pistons are employed, with slide valves resembling in somemeasure those of a high-pressure engine, but having relief valvesto prevent shock at the return of the stroke. Where the engine issingle-acting, with plungers instead of pistons, as in the water-pressure engine already described, the relief valves are greatlysimplified, and indeed are reduced to a single clack in connectionwith each cylinder, opening against the pressure, as the relief valvein the valve ehest of the hydraulic crane. The water engineserected at the lead mines at Allenheads, in Northumberland , pre-sent an example of the utilization of natural falls in this country.These engines are used for the various purposes of crushing ore,