70 Color of the Air and of Deep Waters. 
fect may take place near shore in deep waters, by projecting cliffs or 
high shores. 
It is thus ascertained that when the sun’s light, transmitted through 
water, is not lost in its depth, but is partially reflected by the bot- 
tom, the water is of a green color. 
This effect may arise in deep water, from beds of submarine plants, 
or by myriads of microscopic mollusca, which, covering a vast tex- 
tent of sea, may act upon the light, or even exist in mass sufficient to 
produce a permanent color.* 
The colors transmitted by deep waters cannot be directly observ- 
ed like those of air which are visible among the clouds; observations 
agree on this point. The learned Halley, in descending in a diving 
bell, observed that a ray of light which reached him through a small 
opening closed by glass, gave to the upper part of his hand a rose 
color. Had his hand been white, instead of being itself more or less 
red, the experiment would have been more conclusive. The depth 
to which he descended was probably not more than thirty or forty 
feet, at which the transmitted light could not differ much from yel- 
low, which, mixed with shades of white and with the natural color of 
his hand, would produce a rosy tint. He observed that the under 
part of his hand was green, which must have been occasioned by re- 
flexion from the bottom. 
The bluish green color of crevices in the glaciers is occasioned, 
in the same manner as that of water near shore; if the mass of ice 
was as great and as homogeneous as that of the sea, the interior of 
the crevices would be blue ; but the ice contains air bubbles, particles 
of snow, and fissures which reflect the transmitted light, throwing it 
from one face to another of the crevice until it finds an escape. These 
opake substances in the glacier, produce the same effect as a white. 
surface in the depths of the sea. 
There is on the shore of Capri a grotto which nature seems to 
have constructed to exhibit in all its beauty the green color of the 
sea, and which on this account is called the azure grotto ; it is situ- 
ated under a cliff on the north side of the island. As it could not 
be entered by a common boat, it remained unknown until 1826, 
when two Prussian artists Kopitch and Frisi swam into it, and made 
* The theory of the author derives confirmation from the beautifully green ap- 
pearance of large fish as they turn upon their backs in rising towards the surface, 
and sporting round a ship, during her passage through a dark blue sea.—Trans. 
