It may be supposed that there are few People among us so ignorant, but must necessarily know of what value the Falls of Water are in most Places, as being applicable to mills; which are made after various kinds and forms, according to the different genius and abilities of the mill right; for mill work being in manner infinitely diversified; and had I leisure to comment there on, and give you an account,not only of the vast variety that I have seen and heard of; but (when encouraged) what may yet brought to work by steady stream, and the rotation or circular motion of a water-wheel, it would swell these papers to a much larger volume than was at first designed, and frustrate my intended brevity. I only just hint this to show what use this Engine may be put to in working of mills, especially where coals are cheap.
I have only this to urge, that water in its fall from any determinate height, has simply a force answerable and equal to the force that raises it. So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work; it will be improper to stint or confine its uses and operation in reflect of water-mills.
For the water. Be the mine never so deep, each engine working it 60, 70, or80 foot high by applying or setting the engines one over another, as shall be showed at large hereafter in the following pages, you may by a sufficient number of engines keep the bottom of any mine dry; and when once you know how large your feeder or spring is, it is very easy to know what sized engine , or what number of engines will do your business.
The coals used in this engine is of as little value, as the coals commonly burned on the mouths of the coal-pits are: for an engine of a three inch-bore, or the there about, working the water up 60 foot high, requires a fire-place of not above twenty inches deep and about fourteen or fifteen inches wide, which will occasion so small a consumption, that in a coal-pit it is of no account, as we have experienced. And in all parts of England where there are mines; coals are so cheap, that the charge of them is not to be mentioned when we consider the vast quantity of water raised by the inconsiderable value of the coals used and burnt in so small a furnace. What the quantity of coals used for one engine in a year is, cannot easily be ascertained, because of the different nature of the several sorts of coals.
As for the cure of damps by this engine, the air perpetually crowding into the ash-hole and fire-place, as it is natural for it to do, and with a most impetuous force discharge with the smoke at the top of the chimney, the contiguous air is successively following it; so that not only all steams or vapors whatsoever, that may or can arise, must naturally force its way through the fire and so be discharged at the top with the smoke. But this motion of the fire will occasion the fresh Air to descend from above, down all the pits, and every where else in the mine, but down the chimney; provided you have a heading drift, or passage from all the shafts, or pits inin the same work it matters not; for here will be a perpetual circulation of air, andwith that swiftness, as is hardly to be believed. This I have tried, and know to be true; so leave the ingenious miner to his own judgment. Whether when all the air is in a swift motion, that any stagnation of air (which has always been adjudged the cause of damps) can happen in any pit.