536 
THE SCIENTIFIC MONTHLY. 
‘‘To all this splendor of the western sky mi 
its fires as reflected upon the surface of the wat< 
the dark blue of the sea to the east, the white fo, 
defines upon this gloomy background the pale i 
the sombre and greenish segment of the horizon.” 
“ What spectacle can be more sublime than a sui 
cumuli clouds that nearly always accompany the 
myriad of charming, brilliant and changing colors 
parent bosom of the heaving sea, which seems a duplicate and | 
below. 
In North America the sunsets are particularly gorgeous. Often the entire 
heavens are dappled with clouds tinted with the most brilliant shades of gold, 
crimson, purple, green, and bronze, blendend ani 
variety of the most exquisite shades and colors, add to all this the 
magnificent spectale when the above gorgeous display in the j 
and duplicated in the tranquil bosom of a clear sheet of water, and the result is a 
scene of splendor seldom equalled upon this earth. To all this brilliant display is 
sometimes added broad bands of gold and crimson light, which, starting from the 
point where the setting sun disappeared, diverge and extend across the heavens 
in splendid and magnificent glory for 90°, or more frequently beyond the very 
zenith itself. 
The light which accompanies or is the cause of twilight is occasioned by the 
reflection of the sun’s rays, when below the horizon, from the vapors and minute|.,.^^ 
solid particles floating in the atmosphere, ‘‘and perhaps from the material atoms(|.^^^ ^ 
of the air itself.” It is to this property of reflection possessed by the atmospheri;;,?£'j 
that its illumination is due beyond the direct reach of the rays proceeding fro#'^"2.j^-j;; 
the sun, as under the shadow of clouds and behind opaque objects upon the j 
face, where, unless the light were directed upon some principle of general ( 
sion, intense darkness would prevail.” “ So also a sudden illumination woulj'^S, 
attend the rising of the sun, and instantaneous darkness accompany hfe^ 
setting.” 
“As the sun sets to any point upon the surface of the earth, the atmd>f5® 
phere above this point all around the horizon is illuminated by direct rays, at 
the reflection from so broad an illuminated surface brings down to the earth 
large amount of light, but as the dark shadow of the earth, in consequence I 
the continued sinking of the sun rises higher and higher into the atmosphere 
this locality, the reflected light steadily diminishes and finally disappears wheiU^||^"^?| ^ ^ 
direct rays from the sun reach the higher regions of the atmosphere ^^^ve S S 
horizontal line extended toward the sunset.” “By observing the time afterf|_^|"^|^| 2 ; ^/Up¬ 
setting of the sun to the disappearance of the reflected rays, data 
afforded upon which an approximate estimate may be made of the height of 
atmosphere.” 
InuffS^.J 
•Jlii 
=4ft«8i 
On the Equator the duration of twilight is one hour and twelve minui 
here the sun being upon the equinoctial, and apparently descends vertically, 
