Ossian, than whom few are more abundant in description of the appearance of nature, talks of a blue, dark-blue water. *

In the Norse and Icelandic sagas we find "Ran's couch of deepest blue," "the azure garments of Egir's daughters,"

etc.

Among modern and our own poets, I need but say the blue is the predominant idea, and, lastly, our seamen speak of "blue water" when they are out of soundings, although in the same place they will tell you they have "shipped a green sea."

Some seas have acquired specific names, as the White, Black, Yellow, and Red Seas, and the Gulf of California is called "Vermejo," or Vermilion Sea, by the Spaniards.

APPARENT COLOUR

is due to optical effects; in fine weather the sea seems blue by the reflection of the sky-colour from its surface. This is varied by cloud-shadow, and again the reflection from the bottom may alter the tint, and this, more or less, by its distance from the surface.

As to why the sky is blue, Sir J. Herschel and J. Tyndall consent it is one of the enigmas. The observations of the latter, and his experiments to prove whether it may not be due to molecular polarization are well known.

TRUE COLOUR.

But when we gaze into water, pure and deep, it gives us the idea it is blue, and in this respect it differs from the air; the sky, from a deep valley, or when the air is damp, is much fainter in tint than when it is seen from a height, in fact, as many here know, the higher we go, the darker

* Carthon et passim.

does the sky seem; at very great heights it seems to blacken, as the air becomes rarer; with water the reverse

occurs.

River and lake water has usually a green tint; even the mighty Niagara is grass green; the exception being in that which is of ice origin. The Lake of Geneva, we all know, is very blue, as is also the Rhone, where it leaves it *—and I could give other examples.

Blue is the salt sea colour, but this differs in various parts of the world. In equatorial seas the water is dark blue, in extra tropical seas dark green.

The Mediterranean is deep blue, the Red Sea deeper; I think it is deepest at the Straits of Jubal. The Gulf Stream is indigo blue. Many here know how blue and defined it is; a ship may have her bow in the blue and her stern in the green water. It has been suggested to find the longitude, approximately, by this phenomenon. The Indian Ocean is blue-black, and so is the Japan Current, the Kara Siwo, the Black River."

or

66

Can this be due to the effect produced by the relative quantity of salts these waters contain ?

The salterns of France and Italy are a series of ponds into which the sea-water is admitted, and as evaporation progresses and its density increases, so does the colour of the brine vary. In the ponds next the sea the water is green. This changes until, in those farthest off, where crystallization is ready to commence, the water is deep blue, and where it commences a reddish tint is evident. So constant is this appearance that it guides the salt workers in their operations. †

As a rule, the constituents of the ocean are pretty constant

* I have been told this is due to the impalpable dust of mica suspended in it. In the south of Hampshire I have noticed this red tint at the edges, but found there great quantities of Artemia Salina and Chirocephalus.

in quantity, its specific gravity varying from 1.022 to 1.027,

Many times I have found the water 83° F., and we are assured it is sometimes 95° F. And as sea-water of the same density is 1.029 at 28° F., 1026 at 64° F., and 1·022 at 93° F., it is a pity that these different specimens were not corrected for temperature.

Inland seas, as the Baltic and Black Seas, are not so salt, from the preponderance of river supply over evaporation. Maury says:-" The densest sea-water is off Cape Horn, but it was not corrected for temperature."

Let us say that in the Bay of Biscay there are 3.5 per cent. of salines, 4 in the Gulf Stream, and 4.5 in the Indian Ocean. One cogent reason for thinking that the blue colour of the sea depends on its salineness, is the fact that coppersheathed vessels (men-of-war), cruising about the West Indies (e.g.), from whence the Gulf Stream is fed, suffer more from erosion than in many other places.

No one, I believe, has tried to find out whether the blue colour may be due to polarization caused by the molecules of salt in the water.

I said that certain seas had been so named from the colour of their water, which is, perhaps, not always, but sometimes, so tinted; and I will try to give you the cause of this occurrence in some of them.

THE WHITE SEA.

I have never been there, but infer only that it originally derived its name from the pale grey-green of the water which is common in its vicinity. But white sea is by no means uncommon in the South Pacific. I find in my notes, "The sea, off Paita, whitish, or pale pea-green, . . . . due to vast quantities of minute entomostraca." A very trustworthy observer here, tells me he has again and again sailed in white sea, which he ascribed to spawn, i. e., minute organisms.

Captain Newbold* noticed that, when near Bombay, the sea was milky-white, owing to the presence of innumerable animalcules, some of which were large enough to be visible to unaided sight.

YELLOW SEA.

The Yellow Sea, par excellence, of China is not the only sea which is yellow. Along the coast patches of this yellow water is met with frequently. In some places there is a scum such as one sees on a stagnant pool, which, in calm weather, is thrown up in a thick cream-coloured pellicle. This is not so marked, of course, in a gale.

One observert places its limits at the Formosa Straits, in 25° north latitude, and the Rhio Straits at the equator; but it is of greater extent,

The same yellow sea was noticed by Captain Cook, who tells us that it is found all about the east coast of Australia, and round New Guinea. His sailors called the cause of it, sea-sawdust, and its presence gave an oily look to the water. I have seen and examined it often, and believe it to be, as represented, an alga, Trichodesmium, but not always

sheaf-shaped, sometimes fusiform, and never having a reddish tint. In the sea near the Galapagos Islands, there have been seen, by Captain Colnett and Darwin, stripes of dark yellow water, a few yards only in width, but miles long, the colour caused by little gelatinous balls, say one-fifth of an inch in diameter, in which numerous minute spheroids, of two kinds, are embedded. Darwin says he has no notion what they are. Dr. Wallich says, in the Bay of Bengal he has found yellow water, due either to the Trichodesmium, in spherical balls one-twentieth of an inch in diameter, or as bound sheaves or faggots, one-twelfth to one-twentieth of an inch long, or to masses of diatoms. One form, Rhizosolenia, in dishevelled tufts like floss-silk, one-half to one-and-a-half inches long. Salpæ and hydrozoa feed on this till they impart a tint to the water. Another form, Coscinodiscus Regius, onetwentieth of an inch across, is found in countless myriads during calms, and so bright that single frustules were observable at some distance.

GREEN SEA.

I am not aware of any sea being so named, but sea-water in many places is very green.

This is generally caused by reflection of light from a coral or white sand bottom, and is principally found in the Lagoon Islands, as Keeling Atoll, the Paumotoo group, and such like. The effect of the contrast between the outer blue and the inner green water is much impaired if the atoll is covered with tall trees. One of the most charming is Ducie's Island, which looks like a chaplet thrown on the ocean. It is encircled by a broad fringe of snow-white breakers, and the inside water is vivid emerald.

Nor is it necessary that the lagoon should be shallow; with a depth of even 366 feet the contrast of colour is strongly marked.