MANUFACTURES.

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Manufac- engage the reader’s attention with a description of theturas. several curious contrivances ot this kind which are ratherlocal than general, and many of them more ingeniousthan useful, beside the most valuable of them have beenalready illustrated in our Theoretical Treatise on Hy-draulics. We shall therefore in this place confine ourdescription to only one of them which was some few yearsback erected at one of our Cornwall mines.

Pressure (341.) Pressure engine .—This is an invention of the late

engine. ino-enious Mr. Trevethick, but in principle it does notgreatly differ from other Machines executed in France many years back, and described by Belidor in his Arch.Hydraul. lib. iv. ch. i. Mr.Trevethick’sengine, however,is more complete, and is very ingenious; it was firstemployed at the Druid copper mines in the parish ofPi. xxvii, Illogan near Truro. This engine is represented in plate

Pi S-1. xxvii. fig. 1, where A B is a pipe six inches in diameter,

through’ which water descends from the head to theplace of its delivery, to run off at the adit S through a

fall of thirty-four fathoms in the whole ; that is to say, in

a close pipe down the slope of a hill two hundred fa-thoms long, with twenty-six fathoms fall, then perpen-dicularly six fathoms, till it arrives at B, and thencethrough the engine from B to S two fathoms. At theturn B the water enters into a chamber C, the lowerpart of which terminates in two brass cylinders a and b,in which two plugs or pistons of lead D and E arecapable of moving up and down by their piston rods,which pass through a close packing above, and areattached to the extremities of a chain leading over andproperly attached to the wheel Q, so that it cannot slip.

The leaden pieces D and E are cast in their places,and have no packing whatever, i hey move very easily,and if at any time they should become loose, they maybe spread out by a few blows with,a proper instrument,without taking them out of their places On the sidesof the two brass cylinders, m which D and E move,there are square holes communicating towards F andG, which is a horizontal trunk or square pipe, fourinches wide and three inches deep. AH the other pipes,G, G, and R, are six inches m diameter, except theprincipal cylinder wherein the piston H moves ; andthis cylinder is ten inches in diameter and admits anine-foot stroke. The piston rod works through astuffing box above, and is attached to M N, which isthe pit rod, or a perpendicular piece divided into two,so as to allow its alternate motion up and down,leaving a space between without touching the fixed ap-paratus or great cylinder. The pit rod is prolongeddown into the mine, where it is employed to work thepumps, or if the engine were applied to millwork orany other use, this rod would form the communicationwith the first mover. , ,, ,

K L is a tumbler or tumbling-bob, capable of beingmoved on the gudgeons V from its present position toanother, in which the weight L shall hang over withthe same inclination on the opposite side o the perpen-dicular, and consequently the end Jv wi then be asmuch elevated as it is now depressed.

The pipe R S has its lower end immersed in a cis-tern, by which means it delivers its water without thepossibility of the external air introducing itself; so thatit constitutes a Torricellian column or water barometer,and renders the whole column from A to S effectual;as will be seen in the following view of the operation.

The operation .—Let us suppose the lower bar K V ofthe tumbler to be horizontal, and the rod P O so

situated that the plugs D and E shall lie opposite to Machinery each other, and stop the water way G and F. In this '

state of the engine, though each of these pistons ispressed by a force equivalent to more than a thousandpounds, they will remain motionless, because theseactions being contrary to each other, they are constantlyin equilibrio. The great piston being here shown as atthe bottom of its cylinder, the tumbler is to be thrownby hand into the position delineated in the figure. Itsaction upon O P, and consequently upon the wheel Q,draws up the plug D, and depresses E so that thewater way G becomes open from A B, and that of F tothe pipe R; the water consequently descends from Ato C, thence to G G G, until it acts beneath the piston H.

This pressure raises the piston, and if there be anywater above the piston, it causes it to rise and passthrough F into R. During the rise of the piston (whichcarries the pit rod M N along with it) a sliding block I, \

fixed to this rod, is brought into contact with the tail Kof the tumbler, and raises it to the horizontal position,beyond which it oversets by the acquired motion of theweight L. The mere rise of the piston, if there wereno additional motion in the tumbler, would only bringthe two plugs D and E to the position of rest, namelyto close G and F, and then the engine would stop ; butthe fall of the tumbler carries the plug D downwardsquite clear of the hole F, and the other plug E upwardsquite clear of the hole G These motions require noconsumption of power, because the plugs are in equili-brio, as is above observed.

In this new situation the column A B no longer com-municates with G, but acts through F upon the upperpart of the piston H and depresses it;, while the contentsof the great cylinder beneath that piston are driven outthrough G G G, and pass through the opening at Eand R. It may be observed, that the column whichacts against the piston is assisted by the pressure of theatmosphere, rendered active by the column of waterhanging in R, to which that assisting pressure is equiva-lent, as already noticed.

When the piston has descended through a certainlength, the slide or block at T upon the pit rod appliesagainst the tail K of the tumbler, which it depresses,and again oversets; producing once more the positionof the plugs D E. delineated in the figure, and theconsequent ascent of the great piston H, as before de-scribed. The ascent produces its former effect on thetumbler and plugs ; and in this manner it is evident thatthe alternations will go on without limit, or until themanager shall think fit to place the tumbler and plugsD E in the position of rest; namely, so as to stop thepassage F and G.

The length of the stroke may be varied by alteringthe positions of the pieces T and I, which will shortenthe stroke the nearer they are together; as in that casethey will sooner alternate upon the tail K.

As the sudden stoppage of the descent of the columnA B, at the instant when the. two plugs were both inthe water way, might jar and shake the apparatuswhose plugs are made half an inch shorter than thedepth of the side holes, so that, in such case, the watercan escape directly through both the small cylinders R,this gives a moment of time for the generation of thecontrary motion in the piston and the water G G G,and greatly deadens the concussion which might other-wise be produced. Some former attempts to makepressure engines upon the principle of the steam engine