having a stop-cock; k, a waste steam cock; c, a floating piston attached to a piston-rod; e a pipe which generally

n

is

contains hot water. A water pipe, having a valve at 9 immersed in the well, and delivers the water into the reservoir, through a valve z. The air which accumulates in the receiver escapes at n; d, is the rarifying or exhausting vessel.

The whole being filled with mercury and water, shut the

air-valve k, and open i; the steam from the boiler will rush into the receiver, and after heating the water, it presses on its surface, forcing the mercury up into the exhausting vessel d, where it acts as is shewn in the engraving. The water above c, and in the pipes e, f, will be forced up into the cistern v, in a quantity nearly equal to the space occupied by the steam in the receiver. When the piston has been depressed as far as is necessary for its stroke, the self-acting mechanism attached to its rod, shuts i, and opens k; and the mercury now being at liberty to act by its gravity, descends from the exhausting pipe, and raises the piston to its first position; and the steam which pressed it downwards being allowed to flow into the atmosphere, the fall of the mercury from d, into a, leaves a vacuum in d, into which the water from the well is pressed by the atmosphere, and again fills it. The valve at g, prevents its return to the well in the operation of forcing; and the valve z, prevents its fall from the cistern when the vacuum is made in d.

Newcomen, who is generally considered as the inventor of the atmospheric engine, appears to have been an ironmonger, resident at Dartmouth, in Devonshire; and that he was a man of considerable practical ingenuity, is sufficiently evident from his arrangement of the engine suggested by Dr. Papin.

Savery's engine having failed, from the causes we have already stated, the mines were nearly all at a stand for want of some cheap and efficient machine for the purpose of clearing the more distant workings. About this period Newcomen, having associated himself with John Cawley, a native of the same town, proposed to erect engines capable of supplying this desideratum; and taking the exhausted cylinder of Otto Guericke for a model, applied Papin's mode of producing a vacuum to the above machine.

C

A very simple, and at the same time, ingenious mode of illustrating the operations of an atmospheric steam engine, will be found in the annexed apparatus, employed by Professor Brande, in his lectures at the London Institution.

The glass tube and bulb b is shewn with its piston i; the rod being hollow and closed by a screw c. If steam be generated by the spirit lamp d, the air will speedily be expelled; and after this is effected, the screw c may be closed, and a working stroke produced by artificial condensation.

To understand the action of this machine, we must conceive a hollow tube or cylinder, furnished with a piston, made to fit air-tight, and indeed in all respects similar to a common syringe. At the bottom of this are several apertures: one to communicate with the steam boiler, and furnished with a cock to open and shut the communication at pleasure; another for the admission of cold water; and a third to carry off the condensed steam and ejection water.

A small lateral aperture is also formed with a valve to allow the escape of the air, or permanently elastic gas, which will not condense by the application of cold water: this last is called the snifting clack.

If the piston be now raised to the top of the cylinder, and steam admitted, the air will be ejected by the snifting clack. The steam is then cut off, and the cold water allowed to enter, which condensing, the steam forms a vacuum beneath the piston, which is pressed down with a force proportionate to its diameter.

In a working engine for the draining of mines, the piston rod is attached by a chain to the end of a long lever, working on a fulcrum at the opposite end of which are suspended the rods of the pumps intended to raise the water: the weight of these rods exceeds the weight of the piston so much as to draw it up to the top of the cylinder, and the machine is thus ready for the admission of steam, and the production of an entire stroke. A graphic illustration of this engine is given in the descriptive part of our work.

The first really effective engine on this construction appears from a MS. to which we have already referred, to have been erected at Wolverhampton, near the half milestone leading from Walsingham to that town.

In 1718, the patentees agreed to erect an engine for the owners of a colliery, in the county of Durham, where several hundred horses were employed. Mr. Henry Beighton, who was engaged as an agent in this concern, not approving of the intricate manner of opening and shutting the cocks, for the admission of steam, water, &c. which were then moved by strings and catches, invented by a boy of the name of Potter, employed a hanging bar attached to the great working beam for that purpose.

- The double-acting steam engine does not differ very materially from those we have already described. It was

first suggested by Dr. Falck, who published an account of his invention in 1779. The chief improvement which he introduced was the use of two cylinders, into which the steam was alternately admitted by a common regulator, opening the communication with the steam to one, whilst it shut up the opening of the other. The piston rods were kept (by means of a wheel fixed to an arbor) in a continual ascending and descending motion, in the same manner as the rods of a common air-pump, while the nut, acting in the upright racks, was made to work the pumps, which were thus kept in constant action.

From this it will be seen, that in a double-cylinder engine, where two cranks are used, the fly-wheel, which is usually employed as a magazine of power, may be entirely dispensed with; which, in the reciprocating engine, is an advantage of considerable importance, as the whole power of the engine must, in certain positions of the crank, depend upon the action of the fly-wheel.

The fire wheel of M. Amontons, and the steam wheel of his countryman Deslandes, were very ingenious, though both of them much too intricate for general use. The first of these inventions consisted of a number of buckets placed in the circumference of a wheel, and communicating with each other by very intricate circuitous passages. One part of this circumference was exposed to the heat of a furnace, and another to a cistern of cold water. The communications were so disposed, that the steam produced in the buckets on one side of the wheel, drove the water into buckets on the other side, so that one side of the wheel was always heavier than the other, and this constant addition of weight produced a rotatory motion.

Various attempts have been made at different periods to employ the steam engine in the draining of land. M. François was, we believe, the first who suggested its practical