lation of that part which relates to the steam engine. It occurs in the Transactions of the Royal Society for 1697. After alluding to the inconvenience of forming a vacuum by means of gunpowder, which was one of his early propositions, he recommends the alternately turning a small surface of water into vapor, by fire applied to the bottom of the cylinder that contains it, which vapor forces up the plug in the cylinder to a considerable height, and which (as the vapor condenses, as the water cools when taken from the fire) descends again by the air's pressure, and is applied to raise the water out of the mine.' 49. In 1698 Captain Savery obtained a patent for a new mode of raising water, and communicating motion to a variety of machines by the force of steam; and in the following year a working model of the above engine was submitted to the Royal Society, who then held their sittings in Arundel House. Savery's engine was employed to raise water to a given height by the pressure of the atmosphere, and then to force the fluid up the remaining elevation, by the power of steam acting on the surface. 50. The steam apparatus of captain Savery was usefully employed in the mines for many years, and as it forms the ground-work of both Kier's and Pontifex's vacuum engines of the present day, it may be advisable to furnish a detailed account of its construction : 51. Plate I., fig. 1, STEAM ENGINE, represents a general view of the apparatus as employed for raising water. Two copper boilers are employed; they are set in furnaces of brick-work, so constructed that the flame and heated air can circulate around them to the greatest advantage. 52. In the upper part of each boiler is a small cock, a and b, called gauge-cocks. These, by means of screws, may be removed, in order that two-thirds of the quantity of water which it can contain may be introduced into the large boiler, and that the small boiler may be quite filled. The cocks are then replaced, and a fire is made beneath the great boiler, as represented in the engraving. 53. Two steam-pipes, c and d, proceed from the top of the boiler to the receivers e and f. These communications may be effectually closed, or opened and shut alternately, by an ingenious contrivance, represented on an enlarged scale, in fig. 2. 54. At the extremity of the lever connected with the bent handle g there is a square hole to which a pin is adapted. The upper part of this pin forms a pivot, and works in a cross bar r, which is supported by two screws, y and z, and the lower part passes through the lid of the boiler, having fixed to its extremity a brass plate, called the double slide valve, or regulator. This plate, being ground and fitted with great accuracy to the under surface of the lid of the boiler, prevents the escape of steam through either of the steam orifices, which it may cover; and the attendant, by moving the handle g, is enabled to open and shut alternately the steam passages; or, by stopping the regulator between the utmost limits of its movement, the orifices of both pipes may at the same time be effectually closed. 55. From the lower part of the receivers, e and f, proceed two pipes, h, i, resting on the standards 1 and 2; and to these are screwed two other pipes, 3 and 4, branching off to the chambers k, l, m, n, in which are valves, as exhibited in the engraving. Two other pipes 5 and 6, connect the chambers k, l, m, n, with the pipes o and p. The pipe o, which is called the suctionpipe, has its lower end immersed in a well or reservoir of water; and the pipe p is denominated the force-pipe. 56. The action of this engine is very simple. The steam generated in the large boiler is allowed to accumulate in the upper part, until the attendant conceives that a sufficient quantity is collected to supply the engine. He then, by means of the handle g, removes the regulator from beneath the orifice of the steam-pipe d; this allows the steam to rush from the boiler into the receiver e, whence, driving before it the whole of the air contained in the pipes and the receiver, it passes along the pipe h 3, through the valve k, into the force pipe p, where it communicates with the atmosphere. 57. The air being thus expelled from the receiver, and its place occupied by steam, the attendant closes the communication with the boiler, and places the orifice of the cock r, in such position, that a stream of cold water can be discharged from the cistern s upon the external surface of the receiver. This abstracts from the steam that portion of caloric which is necessary to maintain its elastic state; and as water, on its conversion into steam, is found to occupy a space about 1800 times greater than its former bulk, the condensation of the vapor must necessarily produce within the receiver a vacuum. Nothing, therefore, is left to counterbalance the atmospheric pressure on the surface of the water in which the bulb of the suction-pipe o is immersed; and as this pressure, when the vacuum is perfect, can raise a column of water to the height of thirty-three feet, the water ascends into the receiver, and fills it. 58. The receiver being thus filled, the lower clack-valve closes. If the double slide valve be now removed from the orifice of the steampipe d, the steam will rush from the boiler, and drive the water from the receiver into the forcepipe p, from which it cannot escape on account of the clack-valve k. 59. That steam should press upon a liquid in the same manner as upon a solid piston may to many appear surprising; but it should be recollected that the specific gravity of steam, air, or any of the gases, is less than the specific gravity of liquids, otherwise they could not be maintained in a vaporous or gaseous state; and further, that, as no fluid can descend through one which is much heavier than itself, steam cannot descend through water; the steam, entering into the receiver, must continue ou the surface of the water, pressing upon every portion of it until the water is removed, and the receiver again filled with steam. Therefore, the attendant has only occasion to allow cold water' to flow from the cock r upon its outer surface, to produce, as before, a vacuum, and to fill again the vacant space with water from the well. 60. Having thus exhibited the action of the engine, as far as regards one receiver, it is very easy to conceive that, by means of the two steam-pipes and two receivers, an alternate effect may be maintained, and a constant discharge of water kept up at the top of the force-pipe p. 61. The quantity of steam consumed in maintaining the alternate actions of the engine quickly reduces the water in the boiler; and, as danger might occur from allowing the water to descend too low, the gauge-cocks, a and b, have been judiciously introduced. The gauge-cock a descends within the great boiler to about one-half of its depth; and the cock b, in the small boiler, to within eight inches of the bottom. When the attendant conceives that the great boiler requires to be replenished, he turns the handle of the cock a: if steam issues, the water is below that level, and the boiler must be supplied; but, if otherwise, water alone is discharged. 62. When this trial indicates that a supply is required for the great boiler, the attendant kindles a fire beneath the small, or, as it is called, the subsidiary boiler. By placing this at the side of the large boiler the water within is raised by the waste heat nearly to ebullition; consequently it requires but a small addition of caloric to convert a sufficient quantity into steam to expel the water into the large boiler. The steam which is thus generated, having no opportunity to escape, depresses the water and causes it to ascend up the pipe t, through the clack-valve 3, and along the bent pipe u, into the large boiler; and this discharge continues so long as the surface of the water is above the lower orifice of the pipe t, which is within eight inches of the bottom of the boiler. When it is below that point, the steam, in passing through the clack-valve 3, makes a rattling noise, and indicates that the small boiler requires to be replenished. To effect this the attendant turns the cock v, which, being connected with the inclined pipe w, admits water from the force-pipe. 63. The comparative simplicity of this engine affords a strong inducement for its adoption; but its application is, unfortunately, attended by a great waste of steam, and consequent useless expenditure of fuel. In order to drive the water from the receivers, e and ƒ, into the force-pipe p, we have stated that steam must be admitted upon its surface. This steam possesses a sensible temperature, from 150° to 200°, higher than that of the water; consequently, by contact with it, a considerable portion is condensed, and thereby raises the surface of the water nearly to the temperature of ebullition. The extreme slowness with which caloric descends in fluids allows the water to form a heated stratum between the steam and body of cold water. Then, rapidly accumulating in quantity, the steam, by compression, acquires sufficient force to expel the water into the force-pipe p, and, overcoming the weight of the column contained in the pipe, discharges an equal portion at the top. As the water descends in the receivers a new source of condensation occurs; the steam comes in contact with successive portions of the cold surface of the metal, and, according to professor Robison, not less than eleven-twelfths of that which is generated in the boiler are thus uselessly expended. 64. Another imperfection, which operated against the introduction of this engine into mines, is the limited height to which, by suction, as it is improperly termed, and by the pres sure of the steam, water can be raised. By suction, or, in other words, by the pressure of the atmosphere, water can be raised from twentythree to thirty feet; and, from the nature and strength of the materials of which it is composed, steam should not be applied to force the fluid to a greater height than sixty or seventy,an elevation amounting to about sixteen fathoms. How inadequate this engine must be for the purposes of mining is easily perceived. In Savery's time some of the mines were, perhaps, not less than 100 fathoms deep; and, at the present time, several exceed 200 fathoms, or 400 yards. 65. To render the engine effectual for these depths captain Savery proposed that one should be erected at every fourteen or fifteen fathoms: but the expense of attendants, and the consumption of fuel, added to the annual expenditure for wear and tear, would, in this arrangement, exceed the expense incurred by the employment of horses. Besides, there is a liability that one engine should become deranged; in which case the works must cease, as all the other engines would be rendered ineffectual. 66. In the engines constructed under the authority of Savery's patent it was necessary for a laborer to be in constant attendance for the purpose of turning the cocks, which alternately admitted the steam and condensing water. M. de Moura however effected a considerable improvement in this part of the engine, by constructing a self-acting apparatus for this purpose. 67. M. De Moura's apparatus was made selfacting by a very simple contrivance. It consisted of a float within the receiver, composed of a light ball of copper, which is not loose therein, but fastened to the end of an arm or lever, which is made to rise and fall by the float, while the other end of the arm is fixed to an axis; and consequently, as the float moves up and down, the axis is turned round one way or the other. This axis is made conical, and passes through a conical socket, which is soldered to the side of the receiver, and upon that end of the axis which projecs beyond the socket; and therefore, at the outside of the receiver, is fitted a second arm, which is also moved backwards and forwards by the axis as the float rises and falls. By these means the rising and falling of the surface of the water within the receiver communicates a correspondent motion to the outside, in order to actuate the rest of the gear, which regulates the opening and shutting of the steam and injectioncocks. 68. A small cistern is soldered to the outside receiver; and, being kept full of water, surrounds the joint, or conical socket through which the axis of the float passes: this keeps the axis and socket air-tight. The cistern is constantly kept full of water by means of a small leakage from the force-pipe, through a wooden peg, and the drops are conducted by a packthread down to the cistern. A small weight is applied to the |