Agricola, Georgius, De re metallica, 1912/1950

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              <s>
                <pb pagenum="122"/>
              out of the shallower shafts; similarly at the same season it pours into the
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              lowest tunnel and, meeting a shaft in its course, turns aside to a higher tunnel
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              and passes out therefrom; but in autumn and winter, on the other hand, it
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              enters the upper tunnel or shaft and comes out at the deeper ones. </s>
              <s>This
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              change in the flow of air currents occurs in temperate regions at the beginning
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              of spring and the end of autumn, but in cold regions at the end of spring
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              and the beginning of autumn. </s>
              <s>But at each period, before the air regularly
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              assumes its own accustomed course, generally for a space of fourteen days
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              it undergoes frequent variations, now blowing into an upper shaft or
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              tunnel, now into a lower one. </s>
              <s>But enough of this, let us now proceed to
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              what remains.</s>
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              <s>There are two kinds of shafts, one of the depth already described, of
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              which kind there are usually several in one mine; especially if the mine is
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              entered by a tunnel and is metal-bearing. </s>
              <s>For when the first tunnel is
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              connected with the first shaft, two new shafts are sunk; or if the inrush of
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              water hinders sinking, sometimes three are sunk; so that one may take
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              the place of a sump and the work of sinking which has been begun may be
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              continued by means of the remaining two shafts; the same is done in the
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              case of the second tunnel and the third, or even the fourth, if so many are
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              driven into a mountain. </s>
              <s>The second kind of shaft is very deep, sometimes
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              as much as sixty, eighty, or one hundred fathoms. </s>
              <s>These shafts continue
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              vertically toward the depths of the earth, and by means of a hauling-rope
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              the broken rock and metalliferous ores are drawn out of the mine; for which
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              reason miners call them vertical shafts. </s>
              <s>Over these shafts are erected
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              machines by which water is extracted; when they are above ground the
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              machines are usually worked by horses, but when they are in tunnels, other
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              kinds are used which are turned by water-power. </s>
              <s>Such are the shafts which
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              are sunk when a vein is rich in metal.</s>
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              <s>Now shafts, of whatever kind they may be, are supported in various
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              ways. </s>
              <s>If the vein is hard, and also the hanging and footwall rock, the shaft
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              does not require much timbering, but timbers are placed at intervals, one end
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              of each of which is fixed in a hitch cut into the rock of the hangingwall and
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              the other fixed into a hitch cut in the footwall. </s>
              <s>To these timbers are fixed
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              small timbers along the footwall, to which are fastened the lagging and
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              ladders. </s>
              <s>The lagging is also fixed to the timbers, both to those which screen
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              off the shaft on the ends from the vein, and to those which screen off the
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              rest of the shaft from that part in which the ladders are placed. </s>
              <s>The lagging
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              on the sides of the shaft confine the vein, so as to prevent fragments of it
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              which have become loosened by water from dropping into the shaft and
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              terrifying, or injuring, or knocking off the miners and other workmen who
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              are going up or down the ladders from one part of the mine to another. </s>
              <s>For
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              the same reason, the lagging between the ladders and the haulage-way on
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              the other hand, confine and shut off from the ladders the fragments of rock
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              which fall from the buckets or baskets while they are being drawn up;
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              moreover, they make the arduous and difficult descent and ascent to appear
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              less terrible, and in fact to be less dangerous.</s>
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