above another; C and D, their respective pistons connected by one rod. F is a cylinder, containing a fire in a vessel within it in such a manner, that any air passing between the upper and lower portions of it must go through the fire. This vessel also contains a long cylin der, open at the bottom and directly over the centre of the fire, for the purpose of holding coke or other fuel. This cylinder is covered at the top, and packed air tight when it has served the purpose of permitting the fire to be kindled through it and has been filled with fuel.

The cylinder B is fitted up to answer the purpose of a double stroke forcing pump, or bellows, to drive the air into the upper portion of the vessel F, from whence it passes downwards through the fire for the purpose of consuming the smoke (the fresh fuel being supplied from the reservoir above) in its passage through the more completely ignited cinders below. In this act the air is expanded; and, by means of pipes from the lower portion of F, it is conveyed alternately above and below the piston of the cylinder A. In each pipe is fixed a stop cock or valve, so constructed as to open a passage to the external air, when it shuts the connection with the fire vessel. These cocks are worked by a plug frame.

From this construction it will appear evident, that whatever expansion the air receives, its pressure will operate alike upon the piston of the bellows and of the receiver; and that always in opposition to each other : Hence the power of the stroke will be in proportion to the excess of the area of the receiving piston, over that of the feeding one, multiplied by the expansive force of the contained air, and by the length of the movement.

If, when the engine is well constructed, the expansion of the air in keeping up the fire be not found sufficiently sensible, still the form of the engine is such as to admit of either inflammable gas, oil of tar, or other inflammable

matters, being injected, each stroke, upon the fire; so that all the heat generated by the united combustion may operate without waste; perhaps even a slight sprink. ling of water, either upon, or round the sides of the fire, might answer the purpose. It scarcely need be observed, that a tube connected with a small forcing pump are the only things required for producing these effects.

I remain, Sir,

Your obedient servant,

GEORGE CAYLEY. (18 Nicholson's Journal, p. 260.)

Summary of the rise and progress of the STEAM ExGINE. By the Editor.—I have now given all the information I deem important, on the iron manufacture, and the steam engine. The references I have furnished, will enable the reader to supply the slight deficiencies of information, as they comprise every publication of any character upon the subjects discussed. The summary of the improvements gradually introduced in the theory and practice of the steam engine, and inserted in No. 2 of this volume, p. 217, was printed during my absence in Philadelphia; and unless the errata be corrected, will not in some places be intelligible this reason, I chuse to repeat that summary, with a few additional remarks.

for

1. It does not appear that the theory of the steam engine was ever clearly suggested until the Marquis of Worcester's Century of Inventions in 1663. An old historian, I do not know who, writes concerning Pope Silvester (Silvester 2d) thus: Fecit arte mechanica, orologium, et organa hydraulica, ubi, mirum in modum, per aquæ calefactæ violentiam, implet ventus emergens concavitatem barbati, et permulti foratiles tractus æreæ fistulæ modulatos clameres emittunt. 1 Athenæum, 136. I wish

the compiler had cited, by name, the author of this ac count: this mode of blind reference is a very silly practice.

2. The first person who appears to have reduced the theory of the Steam Engine to actual practice, was Capt. Savary, about 1696. He made a vacuum in a pipe whose lower end descended into water, by condensing steam thrown into a reservoir connected with the pipe; and this permitted the atmosphere to press the water upward to the usual height that will counteract or sustain the atmospheric column: he then forced it upward by the pressure of Steam upon the surface of the water in his receiver, or reservoir.

3. Newcomen and Crawley, in 1712, erected an engine wherein the piston working in a cylinder, was raised upward by the force of Steam; which being condensed by injecting water into the cylinder, a vacuum was formed, and the piston was depressed by the weight of the atmosphere on the top of it, no longer counteracted by the atmosphere underneath it.

In Savary's engine, there was great waste of steam by the condensation occasioned by the water on the surface whereof the steam acted: in Newcomen's engine, there was great loss of time and of fuel, by the cooling of the cylinder by the water injected to condense the steam: the steam also was of no further use, after having raised the piston to the required height. Hence,

4. Mr. James Watt of Glasgow, now of Birmingham, after much reflection and experiment, introduced the following improvements.

He condensed the steam in a vessel separate and at a distance from the cylinder; which is now no longer cooled by the injection-water, as in Newcomen's or the atmospheric engine.

He makes an approximation to a vacuum by pumping

out the air, which always, to a certain degree, accompa nies the steam, and by its elasticity re-acts against the under side of the piston

He keeps the outside of the working-cylinder, hot, by the intervention of steam between it and a casing.

He contrived the parallel motion, by which the piston and the upright rod attached to it and connected with the beam, preserves its perpendicularity during the stroke.

He depressed the piston by letting in steam above and upon it, instead of leaving it to descend by the pressure of the atmosphere, thus doubling the duty performed by the steam, and gaining in power and frequency of stroke.

He kept the top of the piston, hot, by means of a casing between the piston and the outward air; so that the steam let on above, is always of the same temperature with that let in below the piston.

He consumed the smoke of the fuel, by making it pass through and over the red hot coals: thereby converting the carbon and the carburetted hydrogen of the smoke into fuel; and preventing the bottom of the boiler from being covered with soot, which is a non-conductor of heat. He supplied the boiler with the hot-injection water. He applied two pipes or tubes inserted into the boiler at different depths; and furnished with cocks; by means of which, it can be ascertained when the boiler is too full, by its throwing out water, or too empty, by its throwing

out steam.

He improved the method of letting the hot-injection water into the boiler as need required, by opening the valve with a floating stone instead of the ball-cock.

He first gave perfection to the rotatory motion by the Sun and Planet wheels connected with the fly.

He sedulously aimed at perfection in every part of the workmanship of the engine, which in his case became much superior to any antecedent engine.