the erection of tho water-wheel pampa are fixed in the shaft, propisetieneil in size to time quantity of water to be drawn, 10 er 12 Inches In diameter being a very common size, where there is only a moderate Influx. The pumps used in mines do not act at all by atmospheric pressure, its in the came of the common household pumps; they are arrangsel in " lifts," or column's, of considerable height, often Indeed from 20 to 30 fathoms, the water being discharged into cisterns placed at the foot, of each, and ranted entirely by lifting or by pressure. The construction and arrangement of the pump-work forms a very important branch of mining, and one which, from the great depth of our mines, and the vast influx of water so common in them, has been much cultivated in this country, and consequently brought to great perfection. Wooden pumps were formerly common in mines ; but they have for a long while been entirely superseded by iron once, which admit of the lifts being carried to a great height without leaking, or the danger of bursting. The whole column of pumps in a shaft is commonly worked by a single pump-rod, which goes down the middle of it and communicate% with each column by a rod attached to its aide. In order to give a reciprocating motion to the main pump rod, a crank on the axle of the water-wheel is attached to one end of a horizontal rod, the other end of which is fixed to an apparatus termed a " bob," consisting of an upright post moveable on a centre, and firmly braced to a horizontal piece framed into it at the bottom, the further end of which is connected with tho pump-rod. In this manner it will be seen that the rotatory motion of the water wheel is converted into a steady reciprocating motion when commu nicated to the pump-rod, the weight of which is always counterbalanced by a lino box filled with stones, old iron, &c., which is attached to the opposite end of the balance-bob. (See Fig. 6.) As the power of the water-wheels used in*mines is entirely due to the gravity of the water, or the force it exerts in falling through a given space, minus the ends of friction, it is only where a consider able stream can be obtained that water-wheels of sufficient power can be erected ; hut in cases where the supply of water is very limited, and it is practicable to obtain a considerable fall; there is another very ingenious mode of applying it, by which the principle of hydrostatic pressure is called into action. This contrivance is termed the " water pressure engine " and is a good deal used in the German mines, though ouly to a limited extent in this country. The principle consists in giving motion to a piston by the alternate pressure of a high column of water, which having performed its office, the coumiuuication is cut off, and the water in the cylinder escapee. The apparatus is not in fact unlike the working portion of a steam-engine, the hydrostatic pressure of a column of water being substituted for the force of elastic vapour and the reciprocating motion thus produced may be directly applied to set the pumps of a mine in action.
the great abundance of coal which exists in this country, and the cheap rate at which it eau be generally obtained, the steam-engine has long been the great auxiliary of the English miner, and in its present improved state it has greatly contri buted, as before noticed, both to the perfection of our milling system and the enormous extraction of minerals and metallic substances by which our mines are distinguished. in our coal-mines, where the fuel is of scarcely more than nominal value, the steam-engine is the only power ever employed for drainage, and in all deep and extensive works for extraction also. In our copper, tin, and lead mines, on the con
trary, where the carriage of coal renders the use of it more expensive, water-power is always, as far as possible, rendered available. In all the deepest and most extensive mines of this description the steam-engine is however indispensable, aud both the drainage and extraction have been in great measure performed by it, sinee its use has been so greatly economised by the reduced consumption of coal consequent upon late improvements.
The history and progressive improvements of the steam-engine are so intimately connected with its general application to mining pur poses, and consequently with the present perfection which the art of mining has attained, and the vent produce afforded by our mines, that it requires some brief notice here. The efficiency of a steam engine for mining purposes is estimated in Cornwall (where from the great expense of coal, all the late improvements have originated) by the standard termed duty, which accurately and conveniently defines the work performed, with reference to_ the consumption of a given quantity of coaL Thus, by the duty of an engine is expressed the number of pounds (always millions) of water which have been raised through the height of ono foot by time consumption of a bushel of coal, the data for this calculation being the quantity of water discharged from the pumpa in a given time, and the quantity of coal consumed by the engine in the same period. This mode of calculating the efficiency of steam-engines was practised by Watt, who thus estimated the saving of fuel e&cted by his engine compared with the atmospheric engine pre viously In use, one-third of this saving being the remuneration claimed by him for the use of his invention. An admirable system for the registration of time duty and other peculiarities of the engines employed in Cornwall was organised in the year 1813, and this system has been ever since continued, the results being monthly mom-Mined aud pub lished in a convenient form. Tho effect of this system has been to excite an extraordinary degree of competition among the engineers, each of whom strives to improve the duty of his engines in every possible manner. The improvements which thus resulted were so unexpected and so extraordinary as to excite suspicion and incre dulity among those engineers who resided in other parts of England, which have only been removed by the most rigorous scrutiny and experiments.
The progressive improvement of the duty of steam-engines has been very accurately traced by 31r. John Taylor, in his ' Itee,ords of Mining ;' and the following is n summary of the results which he obtained : — The above statement, it should be observed, refers only to the aver age duty, many of the best engines having always greatly exceeded this; and at the present time the duty of the best engines in Cornwall varies from about sixty to eighty millions. In the latter eaae there fore one bushel of coal performs as much work as fifteen bushels effected seventy years ago, or as was accomplished by four till within the last five-and-forty years. When it is stated that some of the most powerful engines in Cornwall consume from three to four thousand bushels of coal per month, that some mines employ several such engines, and that the mere expense of drainage is 12,000/. or 13,000/. per annum, the importance of the improvements above noticed will at once be appreciated.