DOI Page / Citation link:
https://doi.org/10.11588/diglit.18826#0172
120 ON PERSPECTIVE. [LECT. IV.
feded, and even perfpective fails in its application.
We have already obferved, that fome articles are too
minute, or too trivial, to engage the attention of
perfpective: others depend not on mathematical
rules, but on the operations of Nature at large j a
reference to which, will not, I hope, be deemed im-
pertinent. Should we requeft a geometrician to
determine the boundaries of an extenfive profpect,
he would not only find the undertaking more dif-
ficult than he expected, but even abfolutely impof-
fible to ftri£t geometry : for, by geometry he would
prove, that the height of a man being fuppofed five
feet, the extent of his vifion mould be confined by
the horizon at about the diftance of three miles, on
]evel ground: whereas, we really infpect much
farther ; becaufe the fame principle which occafions
twilight (I mean the refraction of the air) elevates
apparently the diftances of the profpedt before us,
and renders them vifible to us, although in fact they
are geometrically below our horizon : much after the
fame manner as a piece of money at the bottom of a
fit velfel is rendered vifible by the accefllon of water.
It is not feldom this fact can be demonftrated
on land, but at fea it is of perpetual utility; for,
hereby the tops of hills and lands are raifed up in
the air, fo as to be difcoverable feveral leagues
further off, than otherwife they would be: and
this refractive power in the air, is more fenfible ac-
cording to the greater diftance wherein it has to act,
and the quality of thofe vapours it contains: to the
very great benefit of fome parts of our globe.
? Very
feded, and even perfpective fails in its application.
We have already obferved, that fome articles are too
minute, or too trivial, to engage the attention of
perfpective: others depend not on mathematical
rules, but on the operations of Nature at large j a
reference to which, will not, I hope, be deemed im-
pertinent. Should we requeft a geometrician to
determine the boundaries of an extenfive profpect,
he would not only find the undertaking more dif-
ficult than he expected, but even abfolutely impof-
fible to ftri£t geometry : for, by geometry he would
prove, that the height of a man being fuppofed five
feet, the extent of his vifion mould be confined by
the horizon at about the diftance of three miles, on
]evel ground: whereas, we really infpect much
farther ; becaufe the fame principle which occafions
twilight (I mean the refraction of the air) elevates
apparently the diftances of the profpedt before us,
and renders them vifible to us, although in fact they
are geometrically below our horizon : much after the
fame manner as a piece of money at the bottom of a
fit velfel is rendered vifible by the accefllon of water.
It is not feldom this fact can be demonftrated
on land, but at fea it is of perpetual utility; for,
hereby the tops of hills and lands are raifed up in
the air, fo as to be difcoverable feveral leagues
further off, than otherwife they would be: and
this refractive power in the air, is more fenfible ac-
cording to the greater diftance wherein it has to act,
and the quality of thofe vapours it contains: to the
very great benefit of fome parts of our globe.
? Very