being open to the condenser. As soon as the piston reaches the bottom of the cylinder, the valves r and t must be shut, and u and q opened; when the steam, being no longer able to get through r, would pass down the pipe p, and enter the lower part of the cylinder through q; meantime,

being open to the condenser by the pipe v, would cause the necessary vacuum above the piston to permit its ascent, which being completed, the valves must be again put into the position shewn in the figure, to produce its descent, and so on. It will be sufficient to state that these valves are operated upon, either by levers passing in a steamtight manner through the side pipes, or that sometimes the spindles of the valves are made to act one through the other in stuffing, as in the present instance, when they are worked by external applications. It is likewise not unfrequent to connect a steam and condensing valve, when they are required to open and shut simultaneously, by an external rod. Motion is communicated to the valves in such engines as are without a fly-wheel, by a rod, or beam, attached to the engine beam, very near to the cylinder end of it, and called a plug-tree; this plug-tree is equipped with certain adjustable projections, called tappets, which strike the levers or handles of the valves, and thus open and shut them at the proper intervals, as they rise and fall with the beam.*

By this most ingenious contrivance no waste of steam arises, excepting in the small aperture between the valves; the friction is likewise much less than cither slides, cocks, or indeed any other kind of valve-the only resistance to their motion being the pressure upon the upper side by the steam, when in their seats. Their cost, compared to that of the slide-valve, is much greater; but as they are not liable to wear, and work with great accuracy, the extra expense does not prevent their very general adoption for large engines.

At the same time Mr. Murray described a new airpump, in which the air in the condenser was discharged

• Millington's Epitome.

(Murray's Air-Pump. 1801.)

from the air-pump without an effort to open the valves, or press through a body of water, and in which the air and water were discharged, separately, in different ways; this he effected by discharging the air alone by one bucket, and the water alone by another, or by an eduction pipe of twenty-eight feet in length. A represents the condenser; B the air-pump; C the air piston; D the air valve which is opened and shut by the working parts of the engine, and

has an elastic rod; E the valve for discharging the air; F the exhausting pipe, having a free communication betwixt the condenser and the top of the air-pump, when the valve D is open; G the eduction pipe; K a bucket for lifting the water upwards, as in a common pump; L a foot valve for preventing a return of the water during the descent of the bucket K; M the barrel of the pump for discharging water alone. This, together with an inspection of the preceding diagram, will serve to show the nature of his invention. The utility of the separate discharge of the air and water is unquestionable; but whether this will compensate for the increased expense and complexity, can only be ascertained in practice. Mr. Murray's scheme, however, has been again made the subject of a patent, a short time ago, by Mr. George Stephenson, of Newcastle.

In the same year (1801) Mr. Bramah obtained a patent for an improvement in the four-way cock, by causing it to make a continuous revolution, instead of a partial one (as. used previously.) By this method, the wear was more regular, which rendered the cock durable, and it was likewise more certain and correct in its action.

Mr. John Nuncarrow's engine, for giving motion to a water-wheel, by a fall obtained by the power of steam, acts upon the same principle as those of Papin and Savery; but as his machine possesses many great advantages over theirs, we shall offer no apology for its insertion.

A is the receiver, which may be made either of wood or iron. BBB B B are wooden or cast-iron pipes, for conveying the water to the receiver, and thence to the penstock. C the penstock, or cistern; D the water wheel; E the boiler, which may be either iron or copper; F is the hot well for supplying the boiler with water; G Gare two cisterns under the level of the water, in which the small bores B B and the condenser are contained. HHH is the surface of the water with which the steam engine and water wheel are supplied; a a is the steam pipe, through which the steam is conveyed from the boiler to the receiver; the feeding pipe, for supplying the boiler

with hot water; ccccc the condensing apparatus; d d the pipe, which conveys the hot water from the condenser to the hot well; e e e valves for admitting and excluding the water; ff the injection pipe, and g the injection cock; h the condenser.

It does not appear necessary to say any thing here on the manner in which this machine performs its operations without manual assistance, as the method of opening the cocks, by which the steam is admitted into the receiver and condensed, will be readily conceived, being somewhat similar to the apparatus for working the valves of the common engine. But it will be necessary to remark, that the receiver, penstock, and all the pipes, must be previously filled, before any water can be delivered on the wheel; and when the steam in the boiler has acquired a sufficient strength, the valve as at c is open, and the steam immediately rushes from the boiler at E into the receiver A; the water descends through the tubes A and B, and ascends through the valve e, and the other pipe or tube B, into the penstock C. This part of the operation being performed, and the valve c shut, that at a is suddenly opened, through which the steam rushes down the condensing pipe c, and in its passage meets with a jet of cold water from the injection cock g, by which it is condensed; a vacuum being made by this means in the receiver, the water is driven up to fill it a second time, through the valves e e, by the pressure of the external air, when the steam valve at c is again opened, and the operation repeated for any length of time that the machine is required to work.

There are many advantages which a steam engine on this construction possesses, beyond any thing of the kind hitherto invented; a few of which the inventor thus enumerates:

1st. It is subject to little or no friction.

2dly. It may be erected at a small expense, when compared with any other sort of steam engine.

3dly. It has every advantage which may be attributed to Boulton and Watt's engines, by condensing out of the