Agricola, Georgius, De re metallica, 1912/1950

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The following is the way of indicating the increase or decrease of the
water
in an underground sump, whether it is pumped by this rag and chain
pump
or by the first pump, or the third, or some other.
From a beam which
is
as high above the shaft as the sump is deep, is hung a cord, to one
end
of which there is fastened a stone, the other end being attached to a
plank
.
The plank is lowered down by an iron wire fastened to the
other
end; when the stone is at the mouth of the shaft the plank
is
right down the shaft in the sump, in which water it floats.
This
plank
is so heavy that it can drag down the wire and its iron clasp and
hook
, together with the cord, and thus pull the stone upwards.
Thus, as
the
water decreases, the plank decends and the stone is raised; on the
contrary
, when the water increases the plank rises and the stone is lowered.
When the stone nearly touches the beam, since this indicates that the water
has
been exhausted from the sump by the pump, the overseer in charge of the
machine
closes the water-race and stops the water-wheel: when the stone
nearly
touches the ground at the side of the shaft, this indicates that the
sump
is full of water which has again collected in it, because the water raises
the
plank and thus the stone drags back both the rope and the iron wire;
then
the overseer opens the water-race, whereupon the water of the stream
again
strikes the buckets of the water-wheel and turns the pump.
As
workmen
generally cease from their labours on the yearly holidays, and

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