bent pressure increases in proportion to the depth attained. How vast must this pressure become at the depth of eight or ten miles, when we reflect that the pressure even of such a light body as our air, equals on the earth 15 lbs. on the square inch-water, when perfectly pure, being 815 times heavier than air! Experiments upon this subject have often been made. It has been common to sink bottles full of fresh water, closely corked, into the ocean, when it has been found that the corks have been driven in, while the fresh water has been replaced by salt, or the bottles have burst with the enormous pressure to which they were thus subjected.

Pieces of light porous wood have been weighted and sunk, and when brought up again have been found to be so condensed in their tissues as to be incapable of floating any more, sinking like stones when thrown back into the water.

In the experiments undertaken by various observers upon the temperature of the deep sea, by sinking ther mometers, accidents repeatedly occur from the pressure of the waters above. What sailors term "water-logged " occurs when a boat or vessel has been sunk beneath the surface, so low as to cause the pressure of the superincumbent water to drive the particles of water into the pores of the wood of which the vessel is made.

Many interesting experiments have been carried on both in our own country and on the Continent, to prove the compressibility and elasticity of water. Although much less compressible than air, or gaseous bodies, it is still capable of diminution or increase in bulk, according as the pressure on its surface is greater or less. At the depth of twenty fathoms, twenty cubic inches of seawater occupy only the space that nineteen occupy at the surface.

In its profound depths the Ocean is darker than the darkest night. No twinkling of the stars gives

variety to the dark expanse overhead; and not even the brilliance of the noonday sun can enliven these gloomy regions. Silent and black, it might be conceived to be the abode of eternal night. It has been a question, how deep it is really possible for daylight to penetrate into the waters? In the clear regions of the tropics-where, however, the utmost brilliancy of natural light is attained the bottom of the ocean, at a depth of many fathoms, may be distinctly seen; and navigators state, that the zoophytes and marine plants may be very clearly beheld, and that they appear most delusively near to the surface. Shells are visible, in parts of the Arctic Ocean, at a depth of eighty fathoms, In the seas around the West India Islands, the bottom is distinctly perceptible at thirty fathoms. Ordinarily, about 700 feet appears to be the extent to which light penetrates into the ocean.

i

The colour of the Ocean has engaged much attention, although not, in some instances, with that amount of entire success which could be desired.

Sometimes it is of a beautiful blue-this is its natural colour; at others, it is emerald-green; sometimes it is even milky, and sometimes red, or of a reddish cast. It has been found in the Arctic seas, that the green hue appears to depend upon the presence of a number of semi-transparent spherical substances, with others resembling small portions of fine hair; and the man who made this discovery noticed, further, that the whales delighted most to feed in these green patches of water.

Another great investigator of natural science, while cruising off the coast of Chili, found the vessel passing through a large area of water, having a pale-red colour. Obtaining a bucketful of this singularly-tinged fluid, and placing a drop or two under the microscope, he found it full of animalculæ, which darted about with great rapidity. A cubic inch contained more than 1000 of them, yet the surface tinged by their bodies

extended for several miles. What an innumerable multitude must have been present in the whole! The ordinary colours of the sea, however, depend in a great measure upon the influence of the water upon light, and not upon any colouring principle diffused or dissolved in them. Perfectly pure water, like pure air, when seen in bulk, appears of a beautiful blue colour; but the least admixture of foreign matter destroys this effect, and renders the colour dirty and variously shaded.

Wherever water is clear and deep, it has the colour natural to it. Professor J. Forbes, in his account of his travels in the Alpine regions, says: "During an expedition which I made upon the ice in the month of September, in a snowstorm, I observed that the snow, being eighteen inches deep, exhibited a fine blue at a small depth (about six inches), wherever pierced by my stick. Nor could this possibly be due to any atmospheric reflection, for the sky was of a uniform leaden bue, and snow was falling at the time." Hence it is probable that blue is the colour of pure water. The exquisite blue colour of the glaciers and crevasses among the Alps is highly remarkable. Professor Bunsen notices that the glaciers of the Johull, in Iceland, present this beautiful appear

ance.

and

The colour, also, of the bed upon which the water lies, greatly influences the appearance presented by it. At Capri, in the Gulf of Naples, are two grottoes, blue green, remarkable for the exquisite colour of the water seen in them. The sea at the Blue Grotto is most remarkably clear to a very great depth, so that the smallest objects may be distinctly seen on the light bottom, at a depth of several hundred feet. All the light that enters the grotto, the opening to which is only a few feet above the level of the sea, in the precipitous rock opening on the surface of the water, must penetrate the whole depth of the sea (probably several hundred feet) before it can be reflected into the grotto

from the clear bottom. means, so deep a blue coloration from the vast body through which it has passed, that the dark walls of the cavern are illumined by a pure blue radiance, and the most differently-coloured objects below the surface of the water are made to appear tinged with blue.

The light acquires by this

In the Green Grotto, the depth is less, and the yellow tint of the subjacent rocks alters the colour of the reflected light from blue to green. Some parts of the Mediter ranean Sea are found to present a reddish or purplish hue; and in a bay on the west coast of Africa, the waters always have almost the appearance of being tinged with blood. In both cases, the effect is due to the colour of the bottom.-Chemistry of Creation.

CHAPTER LIV.

THE OCEAN.-PART II.

THE beautiful phosphorescence, familiar to residents on the seacoast, and well known to fishermen-who call the sea "brimy" when its surface, on being agitated by the air or tide, flashes with phosphorescent light-is generally supposed to be principally due to phosphorescent animalcules.

Sometimes the appearance is so marked, as to form a most curious and splendid spectacle. Waves of heaving fire rise and fall flashing in the dark night with a lustre of indescribable brilliancy, and, as far as the eye can see, an ocean of fire appears to toss its waves, emitting & beautifully pure and pale light. Under the bows of the vessel, or in the waterline in her wake, ripples of flashing brilliancy play, and the path of the ship becomes marked with a long line of moving light. When water is taken from the surface, it possesses the same luminous properties. Sometimes the luminosity has different tints; in tropical waters it is often white as snow, and the

whole surface of the deep appears like a field covered with new-fallen snow.

In the Gulf of Guinea the surface of the water sometimes appears of the most brilliant white. The cause in this instance has been supposed to be vast numbers of small crustaceous animals, which have the singular property of emitting a white light.

Sometimes it is of a ghastly blue, and the appearance then presented is more than ordinarily terrifying to the superstitious. Again, sometimes it is of a fiery red, or even scarlet, as though some marine monster's blood did

"The multitudinous sea incarnadine,
Making the green one red,"

Sometimes, also, the tint is green, and sometimes yellow. In many cases, this power of emitting light appears to be a vital property connected with the existence of marine beings. Dr. MacCulloch, who laboriously investigated this curious and interesting subject, writes: "I believe the power of producing light to be a universal property in the marine tribes; I have never found a species in which it did not exist."

The luminosity of some fishes depends upon the minute phosphorescent creatures (Nereis Noctiluca) attaching themselves to the scales of fish, and thus illuminating the surface of the creature on which they rest. Many of these phosphorescent creatures are of extreme minuteness. Some of these little beings do not exceed the one-thousandth part of an inch in diameter. Millions may be easily contained in a bucketful of seawater. On examination under the microscope, it appears that they possess the power of squeezing out a phosphorescent fluid, which leaves a line of light in the

water.

In the British Seas, these little animalcules are often found congregated together in innumerable millions. Dr. Pring, in a paper communicated to the British