We shall now describe briefly the mo dern modes of working coals a-dipping of, and deeper than, the engine-pit bot tom. One of these consists in laying a working pump barrel with a long wind bore at the bottom of the dovvnset mine, furnished with a smooth rod working through a collar at the top of the working barrel. At one side of this, near the top, a kneed pipe is attached, and from it pipes are carried to the point of delivery, either at the engine-pit bottom or day level. The spears are worked sometimes by rods connected with the machinery at the surtbee ; in which ease the spears, if very long, are either suspended from swing or pendulum rods, or move on friction rollers. But since the action of the spears, running with great velocity the total length of the engine stroke, very soon tears every thing to pieces, the mo tion of the spears under ground has been reduced from 6 or 8 feet,. the length of the engine stroke, to about 15 inches ; and the due speed in the pump is effect ed by the centring of a beam, and the at tachment of the spears to it. The spears are fastened by a strong bolt, which passes through the beam ; and there are several holes, by means of which the stroke in the pumps can be lengthened. or shortened at convenience. The move ment of the spears is regulated by a strong iron quadrant or wheel at the bot tom.
In level free coals, these pumps may be worked by a water-wheel, stationed near the bottom of the pit, impelled by water falling down the shaft, to be discharged by the level to the day (day-level).
But the preferable plan of working under-die coal, is that recently adopted by the /Newcastle engineers (England); and consists in running a mine a-dipping of the engine-pit, in such direction of the dip as is most convenient ; and both coals and water are brought up the rise of the coal by means of high pressure en gines, working with a power of from 80 to 50 pounds on the square inch. These
machines are quite under command, and, producing much power in little space, they are the most applicable for under ground work. An excavation is male for them in the strata above the coal, and the air used for the furnace under the boiler, is the returned air of the mine ventilation. In the dip-mine a double tram-road is laid_; so that while a num ber of loaded curves are ascending, an equal number of empty ones are going down. Although this improved method has been introduced only a few years back, under-dip workings have been al ready executed more than an English mile under-dip of the engine-pit bottom, by means of three of these high-pressure engines, placed at equal distances in the under-dip mine. It may hence be in ferred, that this mode of working is sus ceptible of most extensive application; and in place of sinking pits of excessive depth upon the dip of the coal, at an almost ruinous expense, much of the under-dip coal will in future be worked by means of the actual engine pits. In the Newcastle district, coals are now working in an engine-pit 115 fathoms deep under-dip of the 'engine-pit bottom, above 1600 yards, and fully 80 fathoms of perpendicular depth more than the bottom of the pit.
If an engine-pit be sunk to a given coal at a certain depth, all the other coals of the -coal-field, both above and below the coal sunk to, can be drained and worked to the same depth, by driving a level cross-cut mine, both to the dip and rise, till all the coals are intersected.