arge tracery windows in this material. Great brick gables,
often with the stepped outline known as crows' feet, are an excellent
architectural feature of these German brick-built towns. In parts of
France, also, ornamental brickwork was from time to time made use of,
but not extensively. It is not necessary to go very minutely into the
manufacture of bricks; but perhaps I ought to say a word or two on the
subject. Good brick earth is not simple clay, but a compound substance;
and what is essential is that it should burn hard or, in other words,
partly vitrify under the action of heat. The brick earth is usually dug
up in the autumn, left for the frosts of winter to break it up, and
worked up in the early spring.

The moulding is to a very large extent done by hand, sometimes in a wet
mould, sometimes in a dry sanded mould, and the bricks are first
air-dried, often under some slight shelter, as the rain or frost damages
them when fresh made; and then, when this process has made them solid
enough to handle, they are burned, and sorted into qualities. The
ordinary or stock brick of London and the neighborhood presents a
peculiarity the origin of which is not known, and which is not met with,
so far as I know, in other parts. Very fine coal or cinders is mixed
with the brick earth, and when the bricks are fired these minute
particles of fuel scattered through the material all of them burn, and
serve to bake the heart of the brick. Stock bricks are burnt in a clamp
made of the raw bricks themselves with layers of fuel, and erected on
earth slightly scooped out near the middle, so that as the bricks shrink
they drop together, and do not fall over sideways.

Most other varieties of bricks are kiln burnt. A very large number of
inventions for making bricks by machinery have been patented. If you
have occasion to look through the specifications of these patents, you
will find four or five main ideas appearing and reappearing, and only
here and there an invention which is to some extent different from the
others. A great majority of these inventions include machinery for
preparing the clay or brick earth, so that it may be dug up and filled
into a receptacle and worked up, screened from pebbles, and made fit for
use in a short time, so as not to have to wait a whole winter. This is
done in some sort of pug mill. A pug mill is a machine consisting of a
large cylinder with a central shaft passing through it from top to
bottom. Kni