DOI Page / Citation link:
https://doi.org/10.11588/diglit.18826#0179
lect.iv.] on perspective. 127
traced the retiring made: correfpondent thereto,
obferve, that, the neareft end of any furface which is
in Ihadow, feemsmore deeply fhaded than the further
end; the ihadow in receding being weakened, as it
were diluted, by degrees, and becoming lighter,
and lighter. The very gradual diminution of the
force of the fliadow prevents this from being con-
fpicuous in adjacent parts; but when we com-
pare the extremes, it appears unqueftionable. The
refult is, that a greater ftrength of light, accompa-
nied by a greater Itrength of made, brings for-
ward thofe objects to which it is applied; while a
correfpondent privation of both, or, mutual ad-
vances toward each other, produce the appearance
of receffion, and diftance.
The caufe of this is, perhaps, not very difficult
to affign ; for, if we confider, that the rays of light
are perpetually diverging in every potable direction,
it follows, that in a more extended fpace, there is
room and opportunity for the action and the effect
of a much greater number of fuch rays, than there
can be in a letfer fpace; therefore, although by its
nearnefs to our fight, the hither end of a plane fur-
face appears dark, yet, while the air is illuminated,
it interpofes fo much of its illumination between
the diftances of that plane and our fight, as prevents
the fhadow from arriving at our eye with equal
ftrength. Thus it appears, that the air moderates,
and diminifhes, the refplendence of light, and
that it has the fame effect alfo on the obfcurity of
£hadow, endeavouring, as it were, to impart its
r 2 own
traced the retiring made: correfpondent thereto,
obferve, that, the neareft end of any furface which is
in Ihadow, feemsmore deeply fhaded than the further
end; the ihadow in receding being weakened, as it
were diluted, by degrees, and becoming lighter,
and lighter. The very gradual diminution of the
force of the fliadow prevents this from being con-
fpicuous in adjacent parts; but when we com-
pare the extremes, it appears unqueftionable. The
refult is, that a greater ftrength of light, accompa-
nied by a greater Itrength of made, brings for-
ward thofe objects to which it is applied; while a
correfpondent privation of both, or, mutual ad-
vances toward each other, produce the appearance
of receffion, and diftance.
The caufe of this is, perhaps, not very difficult
to affign ; for, if we confider, that the rays of light
are perpetually diverging in every potable direction,
it follows, that in a more extended fpace, there is
room and opportunity for the action and the effect
of a much greater number of fuch rays, than there
can be in a letfer fpace; therefore, although by its
nearnefs to our fight, the hither end of a plane fur-
face appears dark, yet, while the air is illuminated,
it interpofes fo much of its illumination between
the diftances of that plane and our fight, as prevents
the fhadow from arriving at our eye with equal
ftrength. Thus it appears, that the air moderates,
and diminifhes, the refplendence of light, and
that it has the fame effect alfo on the obfcurity of
£hadow, endeavouring, as it were, to impart its
r 2 own