/'.A--' 
THE SCIENTIFIC MONTHLY. 
535 
so transparent that Venus may sometimes be distinguished at midday, and in the 
interior of Africa night succeeds day almost immediately after sunset. At 
Cumna, Humboldt tells us, twilight lasts but a very few minutes, although the 
atmosphere is higher under the tropics than in other regions. 
In warm countries the presence of humidity in the air not only gives to the 
sky the dark azure tint, but also has the effect of modifying the vital power of 
the solar ray.s. At the Equator it adds to the thousand other wonders of nature 
an incomparably beautiful display of light both at sunrise and sunset. The sun¬ 
set, in particular, affords a spectacle indescribably magnificent—a superiority over 
sunrise attributable to the presence of moisture in the air. This is mbre abund¬ 
ant in Jhe evening, after the heat of the day, than in the morning, when it is par¬ 
tially condensed into dew by the effect of the cooler temperature of night.” 
^‘One of the greatest charms of twilight is the varied and endless gorgeous 
coloring of the clouds, which accompanies the setting of the sun. But it is not 
in our climate that the finest sunsets are seen. The celestial blue of distant moun¬ 
tains, the rose or violet tints which in turn tinge the nearer hills, and the warm 
tones of the soil, harmonize in a marvellous manner, when the sun disappears be¬ 
low the horizon, with the gleaning gold of the West, the red,” purple, gold and 
roseate tints that dapple each cloud, or ‘Hhat crown it in the sky, the dark azure 
of the Zenith, and the more sombre and often, in contrast to the others, greenish 
hue which prevails in the east. In the equinoctial regions these soft and delicate 
tints, joined to the varied aspect of the earth’s configuration and the richness of 
vegetation, produce more striking and gorgeous ” effects than with us. Some¬ 
times light and roseate clouds, fringed with a coppery red, produce peculiar 
effects, similar to certain sunsets in our regions; but whenever the sky is 
clear the shades differ entirely from those of the temperate zone, and present a 
special character. Sometimes, too, the indentations of mountains situated be¬ 
low the horizon, or invisible clouds intercepting a part of the solar rays which, 
after sunset, still reach the elevated regions of the atmosphere, give rise to the 
curious phenomena of crepuscular rays. 
“Then may be seen, starting from the point where the sun has disappeared, 
a series of rays, or rather of diverging” “glories,” “which sometimes extend as 
far as 90°, and even in some instances are prolonged as far as the point opposite 
the sun. Upon tbe ocean, as M. Liais remarks, where the sky near the equator, 
IS free from clouds in the visible part, and when the diverging rays mingle with 
the crepuscular arcs, the play of light assumes a form and brilliance which defy 
all description or pictorial illustration. How, indeed, is it possible to depict com¬ 
pletely the rosy tints of the arc fringed by the crepuscular rays that border the 
segment which is still strongly lighted up from the west, the segment itself being 
tinged with a bright gold hue ? How, above all, is it possible to describe the tint 
of an inimitable blue, different from that of noonday, and occupying that portion 
of the sky which is included between the ordinary azure and the crepuscular arc?” * 
* Flammarions atmosphere. 
