DOI Page / Citation link:
https://doi.org/10.11588/diglit.18826#0028
22 ON PERSPECTIVE [LECT. I.
titv of its ravs is diminished, but alfo their lufrre and
vivacity"; they become feeble, and dim. This is na-
tural to its diftant fituation, confidered limply in
itfelf, and if we advert to the fuperior advantages
poffefled by other objects remaining near the e;e,
we find, not only that they occupy on the retina
much of ihe fpace heretofore occupied by the for-*
mer, but alfo, by the vivacity and ftfength of the
images they raife, they out/Iiine, fo to term it, their
diftant friend ; unlefs, indeed, as in the obfcurity of
night, the nearer objects are dark, while the remote
are ftrongly enlightened.
J proceed now from natural caufes5 to thofe which
are adventitious; the principal of thefe is, the rarity,
or the denfity, of that medium through which objects
are feen. To prove thefe effects demonlirably, I
have only to requeft your recollection, that in the late
foggy weather you could fee, fcarcely further than
you could feel; or, if the eye had ftrength enough
to difcern objects immediately around it, thofe at a
little diftance, were involved in uncertainty. The
objects were in their places; in full proportion ;
and your vifual powers in vigour; but the grofs
medium prevented their ufual perception. This is
an extreme inftance of what is perpetually occurring
around us, in a lower degree.
The air is a very fubtile and transparent fluid, and
in a fmall fpace, or diftance, has no perceivable effect
in difcolouring obje&s; but in objects very remote,
we difcover its power. A mountain at hand, is green,
or brown, the fame mountain feen from afar, is blue;
from hill to hill may be clear, while the lower grounds
(as affording moft vapour) are confufed; the upper
4 part
titv of its ravs is diminished, but alfo their lufrre and
vivacity"; they become feeble, and dim. This is na-
tural to its diftant fituation, confidered limply in
itfelf, and if we advert to the fuperior advantages
poffefled by other objects remaining near the e;e,
we find, not only that they occupy on the retina
much of ihe fpace heretofore occupied by the for-*
mer, but alfo, by the vivacity and ftfength of the
images they raife, they out/Iiine, fo to term it, their
diftant friend ; unlefs, indeed, as in the obfcurity of
night, the nearer objects are dark, while the remote
are ftrongly enlightened.
J proceed now from natural caufes5 to thofe which
are adventitious; the principal of thefe is, the rarity,
or the denfity, of that medium through which objects
are feen. To prove thefe effects demonlirably, I
have only to requeft your recollection, that in the late
foggy weather you could fee, fcarcely further than
you could feel; or, if the eye had ftrength enough
to difcern objects immediately around it, thofe at a
little diftance, were involved in uncertainty. The
objects were in their places; in full proportion ;
and your vifual powers in vigour; but the grofs
medium prevented their ufual perception. This is
an extreme inftance of what is perpetually occurring
around us, in a lower degree.
The air is a very fubtile and transparent fluid, and
in a fmall fpace, or diftance, has no perceivable effect
in difcolouring obje&s; but in objects very remote,
we difcover its power. A mountain at hand, is green,
or brown, the fame mountain feen from afar, is blue;
from hill to hill may be clear, while the lower grounds
(as affording moft vapour) are confufed; the upper
4 part