172. Remarks .

What hath been obſerved on the Solar Sha- dows, hath no Regard to thoſe mentioned here: For it matters not in this Problem, whether the
perſpective Plane be perpendicular, inclined, or
parallel; becauſe in theſe different Situations, the
two Points that are uſed may always be found.

Moreover, it muſt be obſerved, that the third
Problem takes in the Shadows of a ſmall Sight, as well as thoſe of the Sun; but not without this
Difference, that the Plane which in the third
Problem is ſuppoſed parallel to the Sun’s Rays,
ought here to be ſuppoſed to paſs through the
Light whoſe Shadows are ſought.

173. CHAP. VIII.
Of mechanically ſhortning the Operations of
Perſpective.
1. WHEN the perſpective Plane is ſup-
pos’d perpendicular or upright.
Problem I.

109. To find the Repreſentations of Figures in
the Geometrical Plane.

Let O be the Eye, R H the Baſe Line; F and
G the Points denoted with the ſame Letters in
Fig. 10.

Then take a Ruler and faſten to the Point G,
ſo that it may turn about the ſame in ſuch man.