BOOK IX. 371 



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 measure- 

 ments 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 beUows-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 disc^. The inner disc 

 is composed of four segments a palm thick, everywhere two pabns 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 on either side of the wheel. 



