1shaft will reach the bottom of the tunnel when it has
been sunk a further
eight fathoms.
eight fathoms.
A TRIANGLE HAVING ALL ITS ANGLES ACUTE AND ITS THREE SIDES UNEQUAL.
This is the method of the surveyor in measuring the mountain, if the
principal vein descends inclined into the depths of the earth or the transverse
vein is vertical. But if they are both inclined, the surveyor uses the same
method, or he measures the slope of the mountain separately from the slope
of the shaft. Next, if a transverse vein in which a tunnel is driven does not
cut the principal vein in that spot where the shaft is sunk, then it is necessary
for the starting point of the survey to be in the other shaft in which the
transverse vein cuts the principal vein. But if there be no shaft on that spot
where the outcrop of the transverse vein cuts the outcrop of the principal
vein, then the surface of the ground which lies between the shafts must
be measured, or that between the shaft and the place where the outcrop of
the one vein intersects the outcrop of the other.
principal vein descends inclined into the depths of the earth or the transverse
vein is vertical. But if they are both inclined, the surveyor uses the same
method, or he measures the slope of the mountain separately from the slope
of the shaft. Next, if a transverse vein in which a tunnel is driven does not
cut the principal vein in that spot where the shaft is sunk, then it is necessary
for the starting point of the survey to be in the other shaft in which the
transverse vein cuts the principal vein. But if there be no shaft on that spot
where the outcrop of the transverse vein cuts the outcrop of the principal
vein, then the surface of the ground which lies between the shafts must
be measured, or that between the shaft and the place where the outcrop of
the one vein intersects the outcrop of the other.
Some surveyors, although they use three cords, nevertheless ascertain
only the length of a tunnel by that method of measuring, and determine
the depth of a shaft by another method; that is, by the method by
which cords are re-stretched on a level part of the mountain or in
a valley, or in flat fields, and are measured again. Some, however, do
not employ this method in surveying the depth of a shaft and the
length of a tunnel, but use only two cords, a graduated hemicycle18 and a
rod half a fathom long. They suspend in the shaft one cord, fastened
from the upper pole and weighted, just as the others do. Fastened to the
upper end of this cord, they stretch another right down the slope of the mountain
to the bottom of the mouth of the tunnel and fix it to the ground. Then to
the upper part of this second cord they apply on its lower side the broad part
of a hemicycle. This consists of half a circle, the outer margin of which is
covered with wax, and within this are six semi-circular lines. From the
only the length of a tunnel by that method of measuring, and determine
the depth of a shaft by another method; that is, by the method by
which cords are re-stretched on a level part of the mountain or in
a valley, or in flat fields, and are measured again. Some, however, do
not employ this method in surveying the depth of a shaft and the
length of a tunnel, but use only two cords, a graduated hemicycle18 and a
rod half a fathom long. They suspend in the shaft one cord, fastened
from the upper pole and weighted, just as the others do. Fastened to the
upper end of this cord, they stretch another right down the slope of the mountain
to the bottom of the mouth of the tunnel and fix it to the ground. Then to
the upper part of this second cord they apply on its lower side the broad part
of a hemicycle. This consists of half a circle, the outer margin of which is
covered with wax, and within this are six semi-circular lines. From the
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