1the major spaces on
the rod, and those which proceed further, mark the
middle of the intervening space which lies between the others. The
straight lines, which run from the fifth to the sixth semi-circular line, show
nothing further. Nor does the line which measures the half, show anything
when it has already passed from the sixth straight line to the base of the
hemicycle. When the hemicycle is applied to the cord, if its tongue indicates
the sixth straight line which lies between the second and third semi-circular
lines, the surveyor counts on the rod six lines which separate the minor
spaces, and if the length of this portion of the rod be taken from the second
cord, as many times as the cord itself is half-fathoms long, the remaining
length of cord shows the distance the tunnel must be driven to reach under
the shaft. But if he sees that the tongue has gone so far that it marks the
sixth line between the fourth and fifth semi-circular lines, he counts six lines
which separate the major spaces on the rod; and this entire space is deducted
from the length of the second cord, as many times as the number of whole
fathoms which the cord contains; and then, in like manner, the remaining
length of cord shows us the distance the tunnel must be driven to reach
under the shaft.19
middle of the intervening space which lies between the others. The
straight lines, which run from the fifth to the sixth semi-circular line, show
nothing further. Nor does the line which measures the half, show anything
when it has already passed from the sixth straight line to the base of the
hemicycle. When the hemicycle is applied to the cord, if its tongue indicates
the sixth straight line which lies between the second and third semi-circular
lines, the surveyor counts on the rod six lines which separate the minor
spaces, and if the length of this portion of the rod be taken from the second
cord, as many times as the cord itself is half-fathoms long, the remaining
length of cord shows the distance the tunnel must be driven to reach under
the shaft. But if he sees that the tongue has gone so far that it marks the
sixth line between the fourth and fifth semi-circular lines, he counts six lines
which separate the major spaces on the rod; and this entire space is deducted
from the length of the second cord, as many times as the number of whole
fathoms which the cord contains; and then, in like manner, the remaining
length of cord shows us the distance the tunnel must be driven to reach
under the shaft.19
STRETCHED CORDS: A—FIRST CORD. B—SECOND CORD. C—THIRD CORD.
D—TRIANGLE.
D—TRIANGLE.