16682An ESSAY
ſection with F a, will determine a X the Repre-
ſentation ſought.
ſentation ſought.
Remarks.
Although we ſuppoſe the Eye in all the
Problems in this Chapter to be above the per-
ſpective Plane, yet it may likewiſe be under
the ſaid Plane; in which Cafe, the Geometrical
Plane is ſuppoſed above the Objects, as we have
already done on another Occaſion.
1179.Problems in this Chapter to be above the per-
ſpective Plane, yet it may likewiſe be under
the ſaid Plane; in which Cafe, the Geometrical
Plane is ſuppoſed above the Objects, as we have
already done on another Occaſion.
CHAP. VII.
Of Shadows.
FIRST we muſt obſerve, with thoſe who
have already treated on this Subject, that
when a luminous Body is equal to an opaque
Body it enlightens, the Shadow of the ſaid Body
is contain’d between parallel Lines, and con-
ſequently, it is equal upon all parallel Lines
placed at any Diſtance whatſoever beyond the
opaque Body. And when the luminous Body
is leſſer than the opaque Body, the Shadow
thereof, increaſes, and is infinitely augmented.
And on the contrary, when an opaque Body
is leſs than the luminous Body, the Shadow there-
of decreaſes and terminates in a Point.
have already treated on this Subject, that
when a luminous Body is equal to an opaque
Body it enlightens, the Shadow of the ſaid Body
is contain’d between parallel Lines, and con-
ſequently, it is equal upon all parallel Lines
placed at any Diſtance whatſoever beyond the
opaque Body. And when the luminous Body
is leſſer than the opaque Body, the Shadow
thereof, increaſes, and is infinitely augmented.
And on the contrary, when an opaque Body
is leſs than the luminous Body, the Shadow there-
of decreaſes and terminates in a Point.
Now becauſe the Sun is vaſtly greater than
any of the Bodies on the Earth’s Surface it en-
lightens, and is at ſo great a Diſtance therefrom,
therefore its Rays may be conſider’d as being
parallel; and conſequently, the Bodies it ſhines
upon as encloſed between parallels: And this
is the firſt Kind of Shadows I ſhall here explain;
any of the Bodies on the Earth’s Surface it en-
lightens, and is at ſo great a Diſtance therefrom,
therefore its Rays may be conſider’d as being
parallel; and conſequently, the Bodies it ſhines
upon as encloſed between parallels: And this
is the firſt Kind of Shadows I ſhall here explain;
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