lower one is one palm one digit wide. This half of the second lever, the end
of which I have just mentioned, is three palms high and one wide ; it projects
three feet beyond the slot of the post on which it turns ; the other end, which
faces the back wall of the furnaces, is one foot and a palm high and a foot wide.
On this part of the lever stands and is fixed a box three and a half feet
long, one foot and one palm wide, and half a foot deep ; but these measurements vary ; sometimes the bottom of this box is narrower, sometimes
equal in width to the top. In either case, it is filled with stones and earth
to make it heavy, but the smelters have to be on their guard and
make provision against the stones falling out, owing to the constant
motion ; this is prevented by means of an iron band which is placed over
the top, both ends being wedge-shaped and driven into the lever so that the
stones can be held in. Some people, in place of the box, drive four or more
pegs into the lever and put mud between them, the required amount being
added to the weight or taken away from it.
There remains to be considered the method of using this machine. The
lower lever, being depressed by the cams, compresses the bellows, and the
compression drives the air through the nozzle. Then the weight of the box
on the other end of the upper lever raises the upper bellows-board, and the
air is drawn in, entering through the air-hole.
The machine whose cams depress the lower lever is made as follows.
First there is an axle, on whose end outside the building is a water-wheel ;
at the other end, which is inside the building, is a drum made of rundles.
This drum is composed of two double hubs, a foot apart, which are five digits
thick, the radius all round being a foot and two digits ; but they are double,
because each hub is composed of two discs, equally thick, fastened together
with wooden pegs glued in. These hubs are sometimes covered above and
around by iron plates. The rundles are thirty in number, a foot and two
palms and the same number of digits long, with each end fastened into a hub ;
they are rounded, three digits in diameter, and the same number of digits
apart. In this practical manner is made the drum composed of rundles.
There is a toothed wheel, two palms and a digit thick, on the end
of another axle ; this wheel is composed of a double disc8. The inner disc
is composed of four segments a palm thick, everywhere two palms and a
digit wide. The outer disc, like the inner, is made of four segments, and is
a palm and a digit thick ; it is not equally wide, but where the head of the
spokes are inserted it is a foot and a palm and digit wide, while on each side
of the spokes it becomes a little narrower, until the narrowest part is only
two palms and the same number of digits wide. The outer segments are joined
to the inner ones in such a manner that, on the one hand, an outer segment
ends in the middle of an inner one, and, on the other hand, the ends of the
inner segments are joined in the middle of the outer ones ; there is no doubt
that by this kind of joining the wheel is made stronger. The outer segments
are fastened to the inner by means of a large number of wooden pegs. Each
*The rim of this wheel is obviously made of segments fixed in two layers ; the " disc "
meaning the aggregate of segments 9η either side of the wheel.