(Cartwright's Engine. 1797.)

the elasticity of the steam flowing from the boiler through 3; the piston d, being attached to the same rod, is also descending. When the piston b reaches the bottom of the cylinder a, the tail or spindle of the valve k being pressed upwards, opens the valve, and forms a communication between the upper side of the piston and the condenser ; at the same moment the valve r is pressed into its seat by

the descent of the cross arm on the piston, which prevents the further admission of steam from the boiler; this allows the piston to be drawn up to the top of the cylinder, by the momentum of the fly-wheel z, in a non-resisting medium. The piston d is also drawn up to the top of c, and the valve i is raised by the condensed water and air, which have accumulated in e, and in the condenser 9. Αι the moment when the piston has reached the top of the cylinder, the valve k is pressed into its place by the pin or tail striking the cylinder cover; and at the same time the piston b striking the tail of the valve r, opens it; a communication is again established between the boiler and piston, and it is forced to the bottom as before. By the descent of the piston d, the water and air which were under it in the cylinder c, being prevented from returning into the condensing cylinder by the valve under i, are driven up the pipe m, in the box n, and are conveyed into the boiler again through the pipe q. The air rises above the water in a, and when, by its accumulation, its pressure is increased, it presses the float o downwards; this opens the valve p, and allows it to escape into the atmosphere."

This most ingenious machine, it appears, was tried first at Cleveland Street, Mary-le-bonne, and afterwards at Horsleydown, at both of which places it is said to have given great satisfaction. These trials must have been much more decisive than any opinion; and although we have not been able to ascertain further respecting the success of the engines when put in practice, than the simple fact of their having been approved of by the respective proprietors, our own judgment warrants a conclusion, that this plan is admirably adapted to be applied where a small engine is necessary. The mode of condensasion adopted by Mr. Cartwright was considered to be liable to great objection previously to experiment; so much so, that one of the greatest engineers this country ever produced, was heard to state it as his opinion, that "were a pipe to be laid across the Thames, the condensation would not be quick enough to work a steam engine with its full effect." It was shown, however, when tried, that

this opinion was incorrect, as the condensation was very rapid, and the vacuum tolerably good.

Not the least ingenious part of Mr. Cartwright's patent was the metallic piston, which has been of late years very generally used. Though this kind of piston is now somewhat differently modified from his, yet he is entitled to the merit of having first introduced it into use. It has been found to answer extremely well, and frequently works for years without needing any attention, and merely requiring to be kept well greased.

Mr. Cartwright's consists of two rings of brass, of the full size of the cylinder, which are cut into segments, as shewn at 11, and laid one above the other, so as to break joint. The joints, therefore, in the under ring are shewn by dotted lines in the figure; and being thus disposed, the two rings are secured in their places by a top and bottom plate, to which the piston rod is fixed. The segments are pushed against the cylinder by steel springs, shewn

at nn.

A rotative engine is also described in this specification; but we apprehend that practical difficulties would prevent its being ever carried into execution. The axis D in the following cut is fixed in an internal drum or cylinder, to the periphery of which are attached the three pistons H H H, which entirely fill the channel formed between the interior and exterior cylinders; dd are two valves or flaps, which, when shut into the cavities, form a portion of the exterior cylinder, but when open (as drawn) serve as a butment to re

ceive the action of the steam, which being introduced from the boiler through the pipe E, and consequently between the open flap d, and one of the pistons H, when the same piston has passed the lower flap d, it also opens and receives the action of the steam, which enters through G, so that the flaps may at all times relieve each other, without interrupting the operation. Mr. Cartwright does not describe how these pistons and valves are to be made, or, being made, how they are to be kept tight. Two methods only are known, namely, hempen or metallic packing; the first would be soon destroyed by the holes in the sides of the exterior cylinders, formed for a communication with the boiler and condenser, by means of the pipes E F G, and metallic packing would here require too much nicety and expense to be generally useful. But this is not all; the friction of the interior drum would far exceed that of the common engine, which it was intended to supersede; and the flaps, d d, would be liable to knock themselves to pieces by the frequent striking against the drum, as they are thrown forward by the external machinery.

Mr. Jonathan Hornblower's Rotative Engine (for which a patent was obtained in 1798) displays much ingenuity. The vessel in which the steam operates consists of a hollow cylinder, composed of two unequal parts, the smaller section of which is screwed off and on, for the purpose of rectifying and repairing the internal structure. These parts are cast separate, and then screwed together, firm and close, by means of flanches. They are then covered with lids turned also true, and form a figure resembling a drum. A Z are two tubes, which pass through the central openings in the lids of the drum, meeting each other at B. a b c d, are the interior limits of those tubes, on the inside of the drum, which are considerably larger than at A Z in their diameters; the use of which is, that there shall be a proper cavity at e f g h, to receive a packing of tow and grease, or any other materials answering the purpose, between that particular part and the end of the drum; and also the frames of the diaphragms C C, may have the firmer holding to the hollow axles or tubes at D, D, leaving the parts of the diaphragm pendent at i k. The dotted lines show the interior limits of the drum, when the diaphragms are in their places; between which and the extremities of the diaphragms there is a proper rabbet to receive the packing, and between the pendent part of the diaphragms and the central hollow tube about which it revolves. This rabbet is formed by means of plates of metal, screwed on to the frame of the diaphragms, having their edges nearly in contact with the inner surface of the drum, and will be found accessible to repair or renew the packing, when the pannel which constitutes a part of the drum is removed. The parts e f g h may also be repaired at the same time, by means of removing two screws at each end of the hollow tube. The diaphragms (which are here standing in opposite directions) may therefore freely revolve the one after the other, or one may move whilst the other remains stationary. The tubes to which they are attached will have their concentricity preserved by means of the solid axle within the hollow one at E, fig. 2, which is fixed to the