DOI Page / Citation link:
https://doi.org/10.11588/diglit.62828#0089
( 39 )
Second, Take then the fhorteft diameter in the compares,
and place one foot on the fine 90°, and open the feCtor till the
other coincides or touches 90° on the other limb of the inftru-
ment. In this pofition keep the inftrument fixed, and contract
the compares till their feet touch the fine 8o°.8o°; transfer this
opening of the compaifes to the perpendicular line 8 at 8c,
which mark with the point of a pencil.
Proceed to the fine 70, keeping the feCtor ftill in the fame
pofition, and, after contracting the compaifes till their legs touch
70.70 on the fedtor, transfer this opening to the perpendicular
line 7 at 70% and fo on of all the reft to the fine 10, by which
■will be obtained nine points, contracted in due proportion* from
the arch D, A; and a line, palling through each of thefe points,
and drawn by a heady hand, will form an ellipfis perfectly true
and agreeable, as is evident by the figure.
From what has been faid, I prefume it will eafily be under-
ftood by every one how to proceed with the other quarters to
complete the whole ellipfis.
* This is evident by obferving, that as a right line drawn from 45 on the tangent
line to the center 9, cuts the arch D A in the degree 45 ; fo likewife will a right line
drawn from IO on the tangent line to the center, cut the elliptic arch 90 A in the fame
degree.
A circle
Second, Take then the fhorteft diameter in the compares,
and place one foot on the fine 90°, and open the feCtor till the
other coincides or touches 90° on the other limb of the inftru-
ment. In this pofition keep the inftrument fixed, and contract
the compares till their feet touch the fine 8o°.8o°; transfer this
opening of the compaifes to the perpendicular line 8 at 8c,
which mark with the point of a pencil.
Proceed to the fine 70, keeping the feCtor ftill in the fame
pofition, and, after contracting the compaifes till their legs touch
70.70 on the fedtor, transfer this opening to the perpendicular
line 7 at 70% and fo on of all the reft to the fine 10, by which
■will be obtained nine points, contracted in due proportion* from
the arch D, A; and a line, palling through each of thefe points,
and drawn by a heady hand, will form an ellipfis perfectly true
and agreeable, as is evident by the figure.
From what has been faid, I prefume it will eafily be under-
ftood by every one how to proceed with the other quarters to
complete the whole ellipfis.
* This is evident by obferving, that as a right line drawn from 45 on the tangent
line to the center 9, cuts the arch D A in the degree 45 ; fo likewife will a right line
drawn from IO on the tangent line to the center, cut the elliptic arch 90 A in the fame
degree.
A circle