476 
Proceedings of the Boyal Society 
up a great amount of fine whitish solid matter, which gives the water 
along the shore a milky appearance. 
With the assistance of these whitish particles, we understand 
how it is that the brilliant blue-green of this sea depends so much 
on the continuance of sea-breezes. The longer the wave mills 
have been at work the more fine powder has been produced along 
the shore, and more time given for the particles to be carried sea- 
ward, by the wave-mixed and wind-driven waters, and the blue 
green which only extended in a narrow band along the shore, when 
the wind began to blow, is, after a few days of inshore wind, seen to 
extend far to sea. We also understand how it is that the colour near 
shore is so brilliant and so much greener than outside. Near the 
shore there is a greater quantity of white solid matter in suspension ; 
there is therefore more light reflected, and further, the light does 
not penetrate through so great a depth of water, and has not so 
much of the light of the red end of the spectrum cut out, and 
therefore looks greener than the water outside, the light from which 
has to penetrate a greater depth of the absorbing medium. The 
blueness and beauty of the Mediterranean would thus appear to be 
due to the blue transparency of its waters, coupled with the 
presence of white reflecting particles, and the variety in its colour- 
ing to the amount of the suspended particles at different places and 
at different times. 
From this we see the important influence which the geological 
formation of the shore has on the appearance of the water of a sea, 
as it determines the nature of the solid suspended particles. This 
is beautifully illustrated by the difference of colouring in the 
Mediterranean at Mentone and at Cannes. At Mentone, limestone 
is everywhere abundant along the shore, and this limestone, when 
ground up by the waves, produces an extremely fine and white 
powder, which, mixed with the water, causes the sea at Mentone to 
be far more brilliantly coloured than it is at Cannes, where there is 
but little limestone, and the shore is almost everywhere covered with 
sand, the debris of the surrounding rocks. 
In the experiments in the Mediterranean it was found that the 
solid particles were so abundant that they prevented the sun’s 
rays penetrating in a direct line to any great depth. This was 
shown by the illumination of the white surface placed at some 
