Agricola, Georgius, De re metallica, 1912/1950
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              lower one is one palm one digit wide. </s>
              <s>This half of the second lever, the end
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              of which I have just mentioned, is three palms high and one wide; it projects
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              three feet beyond the slot of the post on which it turns; the other end, which
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              faces the back wall of the furnaces, is one foot and a palm high and a foot wide.</s>
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              <s>On this part of the lever stands and is fixed a box three and a half feet
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              long, one foot and one palm wide, and half a foot deep; but these measure­
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              ments vary; sometimes the bottom of this box is narrower, sometimes
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              equal in width to the top. </s>
              <s>In either case, it is filled with stones and earth
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              to make it heavy, but the smelters have to be on their guard and
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              make provision against the stones falling out, owing to the constant
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              motion; this is prevented by means of an iron band which is placed over
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              the top, both ends being wedge-shaped and driven into the lever so that the
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              stones can be held in. </s>
              <s>Some people, in place of the box, drive four or more
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              pegs into the lever and put mud between them, the required amount being
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              added to the weight or taken away from it.</s>
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              <s>There remains to be considered the method of using this machine. </s>
              <s>The
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              lower lever, being depressed by the cams, compresses the bellows, and the
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              compression drives the air through the nozzle. </s>
              <s>Then the weight of the box
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              on the other end of the upper lever raises the upper bellows-board, and the
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              air is drawn in, entering through the air-hole.</s>
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              <s>The machine whose cams depress the lower lever is made as follows.
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              <s>First there is an axle, on whose end outside the building is a water-wheel;
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              at the other end, which is inside the building, is a drum made of rundles.
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              <s>This drum is composed of two double hubs, a foot apart, which are five digits
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              thick, the radius all round being a foot and two digits; but they are double,
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              because each hub is composed of two discs, equally thick, fastened together
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              with wooden pegs glued in. </s>
              <s>These hubs are sometimes covered above and
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              around by iron plates. </s>
              <s>The rundles are thirty in number, a foot and two
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              palms and the same number of digits long, with each end fastened into a hub;
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              they are rounded, three digits in diameter, and the same number of digits
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              apart. </s>
              <s>In this practical manner is made the drum composed of rundles.</s>
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              <s>There is a toothed wheel, two palms and a digit thick, on the end
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              of another axle; this wheel is composed of a double disc
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              8
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              . </s>
              <s>The inner disc
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              is composed of four segments a palm thick, everywhere two palms and a
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              digit wide. </s>
              <s>The outer disc, like the inner, is made of four segments, and is
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              a palm and a digit thick; it is not equally wide, but where the head of the
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              spokes are inserted it is a foot and a palm and digit wide, while on each side
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              of the spokes it becomes a little narrower, until the narrowest part is only
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              two palms and the same number of digits wide. </s>
              <s>The outer segments are joined
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              to the inner ones in such a manner that, on the one hand, an outer segment
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              ends in the middle of an inner one, and, on the other hand, the ends of the
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              inner segments are joined in the middle of the outer ones; there is no doubt
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              that by this kind of joining the wheel is made stronger. </s>
              <s>The outer segments
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              are fastened to the inner by means of a large number of wooden pegs. </s>
              <s>Each </s>
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