17888An ESSAY on
ner, that right Lines drawn along one of its Sides,
may paſs through the Point G. This being done,
faſten one End of a Thread, put through the Eye
of a Needle B, in the Point F; and then put the
ſaid Thread about a Pin faſten’d in the Point O;
ſo that when the Thread is uſing, it may be al-
ways kept tight by means of a Plummet fix’d to
its other End, and freely hanging under the Tube.
Note, The aforeſaid Needle onght to be Braſs or
Silver, ſharp at both Ends, and having its Eye
pretty near one of them.
may paſs through the Point G. This being done,
faſten one End of a Thread, put through the Eye
of a Needle B, in the Point F; and then put the
ſaid Thread about a Pin faſten’d in the Point O;
ſo that when the Thread is uſing, it may be al-
ways kept tight by means of a Plummet fix’d to
its other End, and freely hanging under the Tube.
Note, The aforeſaid Needle onght to be Braſs or
Silver, ſharp at both Ends, and having its Eye
pretty near one of them.
Operation.
Let A be a Point of the Figure to be thrown
into Perſpective. Now place that of the two
Points of the Needle, which is nigheſt to the
Eye thereof, upon the ſaid Point A, and move
the Ruler G E, until it cuts the Thread A F, in
the Point E, wherein the ſaid Thread cuts the
Baſe Line; and then the Point a, wherein the
Ruler cuts the Thread A O, is the Point ſought,
and it may be marked with that Point of the
Needle fartheſt diſtant from its Eye, having firſt
preſſed the Ruler down upon the Paper and Thread,
that ſo the Plummet may not make the Thread
ſlip. And in this manner may any Number of
Points be found. This is demonſtrated in N. 32.
Sometimes it is more convenient to uſe the fol-
lowing Method.
into Perſpective. Now place that of the two
Points of the Needle, which is nigheſt to the
Eye thereof, upon the ſaid Point A, and move
the Ruler G E, until it cuts the Thread A F, in
the Point E, wherein the ſaid Thread cuts the
Baſe Line; and then the Point a, wherein the
Ruler cuts the Thread A O, is the Point ſought,
and it may be marked with that Point of the
Needle fartheſt diſtant from its Eye, having firſt
preſſed the Ruler down upon the Paper and Thread,
that ſo the Plummet may not make the Thread
ſlip. And in this manner may any Number of
Points be found. This is demonſtrated in N. 32.
Sometimes it is more convenient to uſe the fol-
lowing Method.
Method II.
110.
Let O be the Eye, H E the Baſe Line,
11Fig. 61. and F I the Geometrical Line. Take a Ruler
M N, having two Threads equal in Length
faſten’d to it, and about O as a Center, and
11Fig. 61. and F I the Geometrical Line. Take a Ruler
M N, having two Threads equal in Length
faſten’d to it, and about O as a Center, and