or the cases to lie in; form the end
of one spoke to that of another; then tie the cases in the grooves
head to tail, in the same manner as those on the horizontal
water-wheel; so that the cases, successively taking fire from one
another, will keep the wheel in an equal rotation. Two of these wheels
are very often fired together, one on each side of a building, and
both lighted at the same time, and all the cases filled alike, to make
them keep time together; as they will, if made by the following
directions: In all the cases of both wheels, except the first, on each
wheel drive two or three ladlesful of slow fire, in any part of the
case; but be careful to ram the same quantity in each case; and in the
end of one of the cases, on each wheel, you may ram one ladleful of
dead-fire composition, which must be very lightly driven; you may also
make many changes of fire by this method.

Let the hole in the nave of the wheel be lined with brass, and made to
turn on a smooth iron spindle. On the end of this spindle let there be
a nut, to screw off and on; when you have put the wheel on the
spindle, screw on the nut, which will keep the wheel from flying off.
Let the mouth of the first case be a little raised. Vertical wheels
are made from ten inches to three feet diameter, and the size of the
cases must differ accordingly; four-ounce cases will do for wheels of
14 or 16 inches diameter, which is the proportion generally used. The
best wood for wheels of all sorts is a light and dry beech.

_Horizontal Wheels._--They are best when their fells are made
circular; in the middle of the top of the nave must be a pintle,
turned out of the same piece as the nave, two inches long, and equal
in diameter to the bore of one of the cases of the wheel; there must
be a hole bored up the centre of the nave, within half an inch of the
top of the pintle. The wheel being made; nail at the end of each spoke
(of which there should be six or eight) a piece of wood, with a groove
cut in it to receive the case. Fix these pieces in such a manner that
half the cases may incline upwards and half downwards, and that, when
they are tied on, their heads and tails may come very nearly together:
from the tail of one case to the mouth of the other carry a leader,
which should be secured with pasted paper. Besides these pipes, it
will be necessary to put a little meal-powder within the pasted
paper, to blow off the pipe, that there may be no obstruction to th