DOI Page / Citation link:
https://doi.org/10.11588/diglit.18826#0145
106
on perspective. [lECT. iii.
PLATE XXXIV.
To reprefent fhadows caufed by the Sun, Ave muft fix
a point in the picture for the luminary, and, as its feat,
a point on the plane on which the fhadow is to be call:
this is found, by letting- fall a perpendicular from the
luminary; whofe fituation with refpect to the picture we
mall quickly attend to.
No. I. R is a ray from the fun ; I the fpectator's eye ;
of which J is the feat. The rays of the fun being pa-
rallel, a line parallel to R paffing through I gives T for
the place of the fun in the picture ; a line from the feat
of the fun, through the feat of the eye (J) cuts the picture
perpendicularly under T: produce this perpendicular,
till it cuts the horizontal line, as at H, for the vanifhing
point of fhadows on the ground.
C is the center of the picture : if the fun was perpen-
dicular to the plane of the pi£ture, and of confequence
directly at the back of the fpectator I J, the line H T
would become union with the vertical line C G ; as, if the
i'un were on this fide the fpectator, the line H T would be
removed toward L. If the fun was nearer the, horizon,
the point T would be proportionally elevated toward H;
or, if the fun was in the zenith, it would be immediately
over C G, and would occafion no latei'al fhadow.
When the fpectator is betzveen the fun and the picture,
as in this example, the feat of the fun on the picture, as
at T, is below-the. horizontal line; but when the picture
is between the fpectator and the fun, the fun's feat on the
picture, is of neceffity above that line, as has been ex-
plained in the Lecture.
No. II. In this example, the picture is between the fun
and the fpectator : and the«plane on which it is propofed
to find the fhadow is vertical (as E.)
I is the fpectator's eye ; J its feat; R the inclination of
the luminous rays ; S the feat of the luminary on the
ground; and S K the declination of the rays. F is an
object perpendicular to E.
To prepare this picture, firft draw J h parallel to S K,
and at h erect a perpendicular ; then draw I T parallel to
R, cutting" the line from h in T, which is the fun's place
in the picture. C is the center of the picture, through
which produce a perpendicular, as T)d, which is the va-
nilhing line of the perpendicular plane E. Draw T D
perpendicular to T //, then is D the feat of the fun on the
vertical line, and the vanifhing point of fhadows on that
plane ; as H is, on the horizontal line.
PLATE
on perspective. [lECT. iii.
PLATE XXXIV.
To reprefent fhadows caufed by the Sun, Ave muft fix
a point in the picture for the luminary, and, as its feat,
a point on the plane on which the fhadow is to be call:
this is found, by letting- fall a perpendicular from the
luminary; whofe fituation with refpect to the picture we
mall quickly attend to.
No. I. R is a ray from the fun ; I the fpectator's eye ;
of which J is the feat. The rays of the fun being pa-
rallel, a line parallel to R paffing through I gives T for
the place of the fun in the picture ; a line from the feat
of the fun, through the feat of the eye (J) cuts the picture
perpendicularly under T: produce this perpendicular,
till it cuts the horizontal line, as at H, for the vanifhing
point of fhadows on the ground.
C is the center of the picture : if the fun was perpen-
dicular to the plane of the pi£ture, and of confequence
directly at the back of the fpectator I J, the line H T
would become union with the vertical line C G ; as, if the
i'un were on this fide the fpectator, the line H T would be
removed toward L. If the fun was nearer the, horizon,
the point T would be proportionally elevated toward H;
or, if the fun was in the zenith, it would be immediately
over C G, and would occafion no latei'al fhadow.
When the fpectator is betzveen the fun and the picture,
as in this example, the feat of the fun on the picture, as
at T, is below-the. horizontal line; but when the picture
is between the fpectator and the fun, the fun's feat on the
picture, is of neceffity above that line, as has been ex-
plained in the Lecture.
No. II. In this example, the picture is between the fun
and the fpectator : and the«plane on which it is propofed
to find the fhadow is vertical (as E.)
I is the fpectator's eye ; J its feat; R the inclination of
the luminous rays ; S the feat of the luminary on the
ground; and S K the declination of the rays. F is an
object perpendicular to E.
To prepare this picture, firft draw J h parallel to S K,
and at h erect a perpendicular ; then draw I T parallel to
R, cutting" the line from h in T, which is the fun's place
in the picture. C is the center of the picture, through
which produce a perpendicular, as T)d, which is the va-
nilhing line of the perpendicular plane E. Draw T D
perpendicular to T //, then is D the feat of the fun on the
vertical line, and the vanifhing point of fhadows on that
plane ; as H is, on the horizontal line.
PLATE