DOI Page / Citation link:
https://doi.org/10.11588/diglit.62828#0092
( 42 )
is added another of the fame kind, marked T on each limb, but
without a brafs center to it.
To divide a circle by this line, proceed thus:
Take the radius of the circle to be divided, and with this
opening, place the compafs legs on each line T, marked 45.45,
then will the fcdtor be prepared for finding every degree of a
circle up to 45. This is clear; for if the radius be laid down
on the tangent line, Fig. 12, as at 45, a line drawn from 45 to 9,
the center, will cut the arch DA at 45 degrees, as is obvious
by infpedtion. Thus the circle may be divided into eight, fince
forty-five is the half of ninety, confequently the eighth of three
hundred and fixty. The fedtor being ftill in the fame pofition,
if you want to cut the arch DA at 10 degrees, contradh the legs
of the compafles till they coincide with 10.10 on the tangent
line, and transfer this on the tangent line A 45, and a right line
being drawn to the center as before, it will cut the arch D A at
10. Hence if the arch DA is required to be divided into nine,
the extent of the compafles at thofe ten degrees will turn nine
times on the arch D A.
It has already been obferved, that there are two tangent
lines on the fedtor. The tangent line which has not the brafs
center, is to increafe that which has one up to 75, as it is marked
on
is added another of the fame kind, marked T on each limb, but
without a brafs center to it.
To divide a circle by this line, proceed thus:
Take the radius of the circle to be divided, and with this
opening, place the compafs legs on each line T, marked 45.45,
then will the fcdtor be prepared for finding every degree of a
circle up to 45. This is clear; for if the radius be laid down
on the tangent line, Fig. 12, as at 45, a line drawn from 45 to 9,
the center, will cut the arch DA at 45 degrees, as is obvious
by infpedtion. Thus the circle may be divided into eight, fince
forty-five is the half of ninety, confequently the eighth of three
hundred and fixty. The fedtor being ftill in the fame pofition,
if you want to cut the arch DA at 10 degrees, contradh the legs
of the compafles till they coincide with 10.10 on the tangent
line, and transfer this on the tangent line A 45, and a right line
being drawn to the center as before, it will cut the arch D A at
10. Hence if the arch DA is required to be divided into nine,
the extent of the compafles at thofe ten degrees will turn nine
times on the arch D A.
It has already been obferved, that there are two tangent
lines on the fedtor. The tangent line which has not the brafs
center, is to increafe that which has one up to 75, as it is marked
on