BOOK IX.

37i

lower one is one palm one digit wide. This half of the second lever, the endof which I have just mentioned, is three palms high and one wide ; it projectsthree feet beyond the slot of the post on which it turns ; the other end, whichfaces 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 feetlong, one foot and one palm wide, and half a foot deep ; but these measure-ments vary ; sometimes the bottom of this box is narrower, sometimesequal in width to the top. In either case, it is filled with stones and earthto make it heavy, but the smelters have to be on their guard andmake provision against the stones falling out, owing to the constantmotion ; this is prevented by means of an iron band which is placed overthe top, both ends being wedge-shaped and driven into the lever so that thestones can be held in. Some people, in place of the box, drive four or morepegs into the lever and put mud between them, the required amount beingadded to the weight or taken away from it.

There remains to be considered the method of using this machine. Thelower lever, being depressed by the cams, compresses the bellows, and thecompression drives the air through the nozzle. Then the weight of the boxon the other end of the upper lever raises the upper bellows-board, and theair 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 randies.This dram is composed of two double hubs, a foot apart, which are five digitsthick, 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 togetherwith wooden pegs glued in. These hubs are sometimes covered above andaround by iron plates. The randies are thirty in number, a foot and twopalms 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 digitsapart. In this practical manner is made the dram composed of randies.

There is a toothed wheel, two palms and a digit thick, on the endof another axle ; this wheel is composed of a double disc 8 . The inner discis composed of four segments a palm thick, everywhere two palms and adigit wide. The outer disc, like the inner, is made of four segments, and isa palm and a digit thick ; it is not equally wide, but where the head of thespokes are inserted it is a foot and a palm and digit wide, while on each sideof the spokes it becomes a little narrower, until the narrowest part is onlytwo palms and the same number of digits wide. The outer segments are joinedto the inner ones in such a manner that, on the one hand, an outer segmentends in the middle of an inner one, and, on the other hand, the ends of theinner segments are joined in the middle of the outer ones ; there is no doubtthat by this kind of joining the wheel is made stronger. The outer segmentsare fastened to the inner by means of a large number of wooden pegs. Each

8 The rim of this wheel is obviously made of segments fixed in two layers ; the discmeaning the aggregate of segments on either side of the wheel.