Agricola, Georgius
,
De re metallica
,
1912/1950
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is broken and part of the chain or anything else should fall down; he guides
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the bag with a wooden shovel, and fills it with water if it fails to take
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in the water spontaneously. </
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<
s
>In these days, they sew an iron band into the
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top of each bag that it may constantly remain open, and when lowered into
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the sump may fill itself with water, and there is no need for a man to act as
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governor of the bags. </
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<
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>Further, in these days, of those men who stand on
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the floor the one empties the bags, and the other closes the gates of the
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reservoir and opens them again, and the same man usually fixes the large
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hook in the link of the chain. </
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<
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>In this way, three men only are employed in
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working this machine; or even—since sometimes the one who empties the
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bag presses the brake which is raised against the other drum and thus stops
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the wheel—two men take upon themselves the whole labour.</
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<
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>But enough of haulage machines; I will now speak of ventilating
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machines. </
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<
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>If a shaft is very deep and no tunnel reaches to it, or no drift
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from another shaft connects with it, or when a tunnel is of great length and
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no shaft reaches to it, then the air does not replenish itself. </
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<
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>In such a case it
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weighs heavily on the miners, causing them to breathe with difficulty, and
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sometimes they are even suffocated, and burning lamps are also extinguished.
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</
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<
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>There is, therefore, a necessity for machines which the Greeks call
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<
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">πνευματικάι</
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and the Latins
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spiritales
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—though they do not give forth any
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sound—which enable the miners to breathe easily and carry on their work.</
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<
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>These devices are of three genera. </
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<
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>The first receives and diverts into
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the shaft the blowing of the wind, and this genus is divided into three species,
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of which the first is as follows. </
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<
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>Over the shaft—to which no tunnel connects—
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are placed three sills a little longer than the shaft, the first over the front,
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the second over the middle, and the third over the back of the shaft. </
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>
<
s
>Their
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ends have openings, through which pegs, sharpened at the bottom, are driven
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deeply into the ground so as to hold them immovable, in the same way that
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the sills of the windlass are fixed. </
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<
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>Each of these sills is mortised into each
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of three cross-beams, of which one is at the right side of the shaft, the second
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at the left, and the third in the middle. </
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>
<
s
>To the second sill and the second
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cross-beam—each of which is placed over the middle of the shaft—planks
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are fixed which are joined in such a manner that the one which precedes
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always fits into the groove of the one which follows. </
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>
<
s
>In this way four angles
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and the same number of intervening hollows are created, which collect the
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winds that blow from all directions. </
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>
<
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>The planks are roofed above with a
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cover made in a circular shape, and are open below, in order that the wind may
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not be diverted upward and escape, but may be carried downward; and there
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by the winds of necessity blow into the shafts through these four openings.
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</
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<
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>However, there is no need to roof this kind of machine in those localities in
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which it can be so placed that the wind can blow down through its topmost
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part.</
s
>
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