HYDRAULIC PRESSURE EN GINES. A Mr. Glynn brought under the notice of the British Association in 1849 the means of employing high falls ofwater to produce reciprocating motion, by means of a pressure engine ; this latter acted on by the power of a descending column of water upon the piston of a cylinder to give motion to pumps for raising water to a different level, or to produce a re ciprocating motion for other purposes. The pressure engine was calculated to give great mechanical effect in cases where water-falls exist of much too great a height and too small a volume to be practically used efficiently on water wheels within the ordinary limits of di ameter. One of these engines is at pres ent worked at the Allport Mines, Derby shire. The cylinder is 50 inches di ameter, and the stroke 10 feet, worked by a column of water 132 feet high, so that the proportion of power to act on it was the area of a piston to that of the plunger, namely, 1,963 to 1,385, or fully 70 per cent. The engine lever cost 60 dollars a year since its erection in 1841. Its usual speed is 5 strokes per minute, but can work 7 without any concussion in the descending column. The duty ac
tually -done being equal to 163 horse power. Area of plunge 9.621 feet X 10 -:- 7 strokes = 673.41. 673.41 X 62.5+132 = 507n 2 = 163 horse power.
Iu this engine as in others, when water acts by its gravity or pressure, these ma chines do the best work when the water enters the machine without shock or im pulse, and leaves it without velocity, obtaining thus all the available power that the water can yield with the least loss of effect. This result is best accom plished by making the pipes and passages of sufficient size to prevent acceleration of the hydrostatic column.
The pressure of a small column of wa ter, as that of a common hydrant pipe, has been made to turn a coffee-mill, which it works economically and efficiently. There are many small machines which might readily be turned by the Croton water in New York, and also in other large cities by the mere descending force of the small hydrant or hose pipe. It would be in cities one of the simplest and least expensive powers.