Where the Amazon, the La Plata, the Orinoco, and other giant streams pour out their vast volumes of water into the ocean, the surface of the sea is fresh for many miles from the shore; but this is only superficial, for below, even in the bed of the rivers, the bitterness of salt water is found. It is a curious fact, that in many parts of the ocean, fresh-water springs burst from the bottom of the sea. Thus, in the Gulf of Spezzia, and in the port of Syracuse, large jets of fresh water mingle with the brine; and Humboldt mentions a still more remarkable submarine fountain on the southern coast of Cuba, in the Gulf of Xagua, a couple of sea miles from the shore, which gushes through the salt water with such vehemence, that boats approaching the spot are obliged to use great caution. Trading vessels are said sometimes to visit this spring, in order to provide themselves in the midst of the ocean with a supply of fresh water. * * * * * The sea is not colourless; its crystal mirror not only reflects the bright sky or the passing cloud, but naturally possesses a pure bluish tint, which is only rendered visible to the eye when the light penetrates through a stratum of water of considerable depth. This may be easily ascertained by experiment. Take a glass tube, two inches wide and two yards long, blacken it internally with lamp-black and wax to within half an inch of the end, the latter being closed by a cork. Throw a few pieces of white porcelain into this tube, which, after being filled with pure sea-water, must be set vertically on a white plate, and then, looking through the open end, you will see the white of the porcelain changed into a light blue tint.