Full text: Gravesande, Willem Jacob: An essay on perspective

on PERSPECTIVE. after which, I ſhall touch upon thoſe continually
increaſing. What I ſhall ſay on this Matter, is
ſufficient for deſigning the Shadows of right-lin’d
Bodies; as to the Shadows of other Bodies, it
is ſo difficult to determine them Geometrically
that it is much better to examine thoſe which are
daily obſerved, and ſo imitate them.

I ſhall not ſay any thing concerning Shadows
terminating in a Point, becauſe their Variety
is ſo great, that they cannot be geometrically de-
termin’d. Beſides, Painters ſcarcely ever ſup-
poſe their perſpective Planes or Pictures en-
lightned after this third Manner, unleſs only
when they have a Mind to repreſent a Chamber,
wherein the Light enters through the Windows; but then the Number of Windows, their Situati-
on, and the different Reflections that the Light
ſuffers in the Chamber, produce ſo many dif-
ferent Alterations, that a Painter had better
imitate them, than have recourſe to Rules that
do not take in all Caſes. I ſhall likewiſe be ſi-
lent as to the clair-obſcure, for a ſmall Atten-
tion to daily Experience will better illuſtrate
this Matter than a long Diſcourſe thereon. Be-
ſides, it is impoſſible to furniſh general Rules
on this Subject; and likewiſe the vaſt Number
of Figures, will not permit us to ſeparately
examine them; add to all this, that a Painter
to draw the clair-obſcure, he ought to have, not
only regard to the Figures of Objects, but likwiſe
to their Colour and Matter.

165. Of Solar Shadows.
Problem I.

103. To find the Perſpective of the Shadow of a
Point above the Geometrical Plane, whoſe Height and
Seat is given.

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