sometimes equal, yea exceed the _ordinary_
charge of the whole _Adit_.

Amongst the _Expedients_ that have been devised to remedy this, there is
one practised in the _Coal-mines_, near the Town of _Liege_ (or _Luyck_)
that seems preferable to all others for Efficacy, Ease, and Cheapness: the
description whereof followeth.

At the mouth or entry of the _Adit_ there is a structure raised of _Brick_,
like a _Chimney_, some 28. or 30. foot high in all: at the bottom, two
opposite sides are (or may be) some 51/2 foot broad; and the other two, 5.
foot: the wall 11/2 _Brick_ thick. At the lower part of it, is a hole, some
9. or 10. inches square, for taking out of the Ashes, which when it is
done, this Ash-hole is immediately stopt so close, as Air cannot possibly
get in at any part of it. Then, some 3. foot above ground or more, there is
on that side, that is next to the _Adit_ or Pit, a square hole of 8. or 9.
inches every way, by which the Air enters to make the Fire burn: Into this
hole there is fixed a square _Tube_ or _Pipe_ of Wood, whereof the Joints
and Chinks are so stopt with Parchment pasted or glewed upon them, that the
Air can no where get in to the Pipe but at the end: And this Pipe is still
lengthened, as the _Adit_ or Pit advanceth, by fitting the new Pipes so, as
one end is alwaies thrust into the other, and the Joints and Chinks still
carefully cemented and stopt as before. So the Pipe or Tube being still
carried on, as near as is necessary, to the wall or place, where fresh Air
is requisite; the Fire within the Chimney doth still attract {81} (so to
speak) Air through the Tube, without which it cannot burn, which yet it
will do, as is obvious to conceive (all Illustrations and Philosophical
Explications being here superfluous,) and so, while the Air is drawn by the
fire from the farthest or most inward part of the _Mine_ or _Adit_, fresh
Air must needs come in from without to supply the place of the other, which
by its motion doth carry away with it all the ill vapors, that breath out
of the ground; by which meanes the whole _Adit_ will be alwaies filled with
fresh Air, so that men will there breath as surely as abroad, and not only
Candles burn, but Fire, when upon occasion there is use for it for breaking
of the Rock.

Now that there may be no want of such fresh Air, the Fire must alwaies be
kept burning in the Chimney, or at least as frequently as is necessary: For
which purpose there must be two of th