1always drives forward another, they penetrate into the
tunnel and change
the air, whereby the miners are enabled to continue their work.
the air, whereby the miners are enabled to continue their work.
If heavy vapours need to be drawn off from the tunnels, generally three
double or triple bellows, without nozzles and closed in the forepart, are placed
upon benches. A workman compresses them by treading with his feet, just
as persons compress those bellows of the organs which give out varied and
sweet sounds in churches. These heavy vapours are thus drawn along the
air-pipes and through the blow-hole of the lower bellows board, and are
expelled through the blow-hole of the upper bellows board into the open
air, or into some shaft or drift. This blow-hole has a flap-valve, which the
noxious blast opens, as often as it passes out. Since one volume of air con
stantly rushes in to take the place of another which has been drawn out by
the bellows, not only is the heavy air drawn out of a tunnel as great as 1,200
feet long, or even longer, but also the wholesome air is naturally drawn in
through that part of the tunnel which is open outside the conduits. In this way
the air is changed, and the miners are enabled to carry on the work they have
begun. If machines of this kind had not been invented, it would be necessary
for miners to drive two tunnels into a mountain, and continually, at every
two hundred feet at most, to sink a shaft from the upper tunnel to the
lower one, that the air passing into the one, and descending by the shafts
into the other, would be kept fresh for the miners; this could not be done
without great expense.
double or triple bellows, without nozzles and closed in the forepart, are placed
upon benches. A workman compresses them by treading with his feet, just
as persons compress those bellows of the organs which give out varied and
sweet sounds in churches. These heavy vapours are thus drawn along the
air-pipes and through the blow-hole of the lower bellows board, and are
expelled through the blow-hole of the upper bellows board into the open
air, or into some shaft or drift. This blow-hole has a flap-valve, which the
noxious blast opens, as often as it passes out. Since one volume of air con
stantly rushes in to take the place of another which has been drawn out by
the bellows, not only is the heavy air drawn out of a tunnel as great as 1,200
feet long, or even longer, but also the wholesome air is naturally drawn in
through that part of the tunnel which is open outside the conduits. In this way
the air is changed, and the miners are enabled to carry on the work they have
begun. If machines of this kind had not been invented, it would be necessary
for miners to drive two tunnels into a mountain, and continually, at every
two hundred feet at most, to sink a shaft from the upper tunnel to the
lower one, that the air passing into the one, and descending by the shafts
into the other, would be kept fresh for the miners; this could not be done
without great expense.
There are two different machines for operating, by means of horses, the
above described bellows. The first of these machines has on its axle a
wooden wheel, the rim of which is covered all the way round by steps; a
horse is kept continually within bars, like those within which horses are held
to be shod with iron, and by treading these steps with its feet it turns the wheel,
together with the axle; the cams on the axle press down the sweeps which
compress the bellows. The way the instrument is made which raises the
bellows again, and also the benches on which the bellows rest, I will explain
more clearly in Book IX. Each bellows, if it draws heavy vapours
out of a tunnel, blows them out of the hole in the upper board; if they are
drawn out of a shaft, it blows them out through its nozzle. The wheel has
a round hole, which is transfixed with a pole when the machine needs to be
stopped.
above described bellows. The first of these machines has on its axle a
wooden wheel, the rim of which is covered all the way round by steps; a
horse is kept continually within bars, like those within which horses are held
to be shod with iron, and by treading these steps with its feet it turns the wheel,
together with the axle; the cams on the axle press down the sweeps which
compress the bellows. The way the instrument is made which raises the
bellows again, and also the benches on which the bellows rest, I will explain
more clearly in Book IX. Each bellows, if it draws heavy vapours
out of a tunnel, blows them out of the hole in the upper board; if they are
drawn out of a shaft, it blows them out through its nozzle. The wheel has
a round hole, which is transfixed with a pole when the machine needs to be
stopped.
The second machine has two axles; the upright one is turned by a horse,
and its toothed drum turns a drum made of rundles on a horizontal axle;
in other respects this machine is like the last. Here, also, the nozzles of
the bellows placed in the conduits blow a blast into the shaft or tunnel.
and its toothed drum turns a drum made of rundles on a horizontal axle;
in other respects this machine is like the last. Here, also, the nozzles of
the bellows placed in the conduits blow a blast into the shaft or tunnel.
In the same way that this last machine can refresh the heavy air of a
shaft or tunnel, so also could the old system of ventilating by the constant
shaking of linen cloths, which Pliny20 has explained; the air not only grows
shaft or tunnel, so also could the old system of ventilating by the constant
shaking of linen cloths, which Pliny20 has explained; the air not only grows