In 1841 Mr. John Taylor, well known for his long experience in mining operations, and whose application of water-wheels to the working of pumps has already been mentioned, advised the employment of another and more powerful engine at the Alport mines, near Bakewell, which was made under the author's direction, at the Butterley works. This was the most powerful engine of the kind that had been made. The cylinder is 50 inches in diameter, and the stroke 10 feet. It is worked by a column of water 132 feet high, acting below the piston, and lifting, by direct action, a weighted plunger-pole, 42 inches in diameter, which raises the water from the mine to a height of 132 feet; so that the proportion of power to effect is as the area of the piston to that of the plunger: namely, 1963 to 1385, or full 70 per cent. (See figs. 34, 35, and 36.)

Mr. Darlington, who has the care of the machinery at the mines, and who fixed this engine in the shaft, in a letter to the author, says that the engine has never cost them £12 a year since it was erected.

The usual speed is about five strokes per minute, but it will work at the rate of seven strokes, without any concussion in the descending column; the duty actually done

being then equal to 168 horses' power of 33,000 pounds, raised one foot high in a minute. Thus the area of the plunger, 3 feet 6 inches in diameter, is 9.621 square feet × 10 feet, the length of stroke, × seven strokes per minute = 673.47 cubic feet raised 132 feet high in a minute; and 673-47 cubic feet of water x 62.5 pounds, the weight per foot 132 feet in height = 5,556,127, which divided by 33,000, gives 168, say 168 horses' power. The pressure upon the piston from a column of water, 132 feet high, reckoning 27 inches of water equal to a pound, is about 58 pounds on the square inch, or rather more than 50 tons' pressure on the area of the piston. Thus the area of the piston, 50 inches in diameter, is 1963 square inches × 58 pounds 113,854: and this divided by 2240, the number of pounds in a ton, gives 50.8, say 50 tons.

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There are five other pressure-engines at these mines of smaller size.

This engine was erected early in 1842, and is now working. It was at work, without intermission, for six years; and on one occasion, when the author made inquiry as to its performance, the answer was, that it had been constantly going for the last seventeen weeks, and nobody had seen it during the time.

An excellent working model of this engine will be found in the Museum of Practical Geology in Jermyn-street, London, an institution which ought to be visited by all persons who are interested in mining and metallurgy, and in the employment of mineral wealth for all purposes of practical utility and decorative ornament, as well as by geologists. The model was made by Mr. Jordan, since so well known by his invention for carving wood and stone by machinery, and thus copying works of art.

It will be observed that after the large valves are closed, the pressure is continued upon the piston to complete the stroke. This was at first done by means of cocks; but as the friction of these caused some little trouble, Mr. Darlington substituted some small pistons to shut off the water at the termination of the stroke.

Mr. Taylor has since had another engine of the same size made for a lead mine in Wales, and the results have been equally satisfactory.

In these machines, as in all others where the water acts by its gravity or pressure, the best results are obtained where the water enters them without shock or impulse, and

We then realise all the

quits them without velocity. available power the water will yield, with the least loss of effect; and the duty is best performed by making the pipes and passages of sufficient and ample size to prevent acceleration of the hydrostatic column.

The cranes worked by water-pressure, constructed by Mr. William George Armstrong, of Newcastle-on-Tyne, have been described in another book, on Cranes and Hoisting Machinery, written by the author of this work.

These hydraulic cranes are characterised by their great steadiness and precision of movement. By means of the regulating handles, their motions, both in lifting and lowering, as well as in turning, are graduated with perfect accuracy; and, practically speaking, the speed with which they may be worked has no other limit than that imposed by the size of the supply pipe.

The author has the satisfaction to state that since the treatise on cranes was published, many of those worked by water-pressure have been erected, in and about London,particularly in the collier basin of the West India Docks, where they are used to discharge the cargoes of the ships, and at the Great Western Railway goods station. They are also to be used at the Great Northern and the Camden Town goods stations.

Hydraulic pressure admits of very extensive and useful application in mercantile docks, not only to cranes for lifting heavy weights, but also for "whipping" light goods from ships, and for opening and shutting dock-gates, swingbridges, and sluices.

The facility with which water may be conveyed to the places where the power is wanted, the ease with which it may be managed, its perfect safety, and its constant readiness for action, render it eminently suitable for these purposes.

When hydraulic engines are extensively used and systematically employed, it may be prudent to apply steam power to raise the water to an elevated tank, not less than 100 feet above their level, for that is in reality only another mode of using steam power, the water being the vehicle for its transmission. But there are many places where the supply may with advantage be obtained from the public water-works, and even when the water pressure may be used in transitu, without using the water. This is now actually done in Newcastle-on-Tyne, where an improved pressure

engine, made by Mr. Armstrong, is used to print the Newcastle Chronicle, one of the most extensively circulated provincial newspapers. The author had the pleasure of seeing it in full work. The town is placed on the side of a high and steep hill, and the printing-office is about half-way up, so that the water merely passes through the engine and goes on to aid the supply for the lower parts of the town.

In many parts of London water is supplied, in quantity, at 4d. for 1000 gallons, at a pressure of 150 feet; and there are many trades that require occasionally to use mechanical power, but cannot employ a steam engine, for they do not want the power constantly, and they do not want much power at any time.