mortar in the joints, which
are to be seen perfectly open, as if they had been raked out, in old
brickwork, and in some cases (happily not in many) the action of weather
destroys the bricks themselves, the face decaying away, and the brick
becoming soft.

Against this serious defect in our staple building material a series of
precautions have been devised. Damp rising from the foot of the wall, or
from earth lying round its base, is combated by a damp course--a bed of
some impervious material going through the wall. Damp earth may be kept
off by surrounding the walls with an open area or a closed one--usually
termed a dry area. Damp against the face of the walls may be partly
combated by a careful selection of a non-absorbent brick with a hard
face and by struck joints. But it is most effectually kept at bay by the
expedient of building the wall hollow; that is to say, making the
external wall of the house to consist of two perfectly distinct walls,
standing about 2 in. apart, and held together by ties of earthenware or
iron. The result is that the moisture blowing through the outer skin
does not pass the cavity, but trickles down on the inner face of the
outer wall, while the inner wall remains dry. The ties are constructed
of shapes to prevent their conducting water themselves from without to
the inner wall. In addition to this, a series of slates forming an
intermediate protection is sometimes introduced, and forms an additional
and most valuable screen against weather. Sometimes, the two skins of
the wall are closer together--say 3/4 in.--and the space is filled with a
bituminous material.

A substance of a bituminous nature, called hygeian rock, has been of
late years introduced, and is being extensively used for this purpose;
it is melted and poured into the open space hot, and quickly hardens.
The use of such a material is open to the objection that no air can pass
through it. The rooms of our houses are receiving air constantly through
the walls, and much of the constant current up our chimneys is supplied,
to our great advantage, in this very imperceptible manner. The house
breathes, so to speak, through the pores of its brickwork. When this is
rendered impossible, it seems clear that fiercer draughts will enter
through the chinks and crevices, and that there will be a greater demand
upon flues not in use, occasioning down draught in the chimneys.

Another mode of keeping out weather is to cement the face of