Interesting Facts About the Mighty Deep.

Kaipara and Waitemata Echo, 10 July 1914, Page 8

Interesting Facts About the Mighty Deep.

From ordinary considerations it would seem that there is no limit to the depths to which a diver or a submarine boat mi&ht go. Such, however, i's not the case. What prevents diving to great depths is the enormously increasing pressure of water. No diver without a suit can go over one hundred and fifty feet, because the pressure is then about five tons to the square foot on hi's body—-eardrums would he staved in, and other fearful dilnculties would result.

To remedy this the diving suit was invented ; but there is a limit also to its depth. At a, depth of one mile the pressure due to the water alone is a hundred and sixtyfive tons to the square foot. Even if a diving suit was devised to withstand this enormous pressure, trouble would be found in getting a pipe line that long, and withstanding the same pressure, that would not break of its own weight.

Let us take the extreme depth of the sea so far found, that of five miles, and find the pressure to the square foot on the bottom. As water is comparatively incompressible, a cubic foot of it weighs practically the same on the surface as at the bottom of the sea. In the case of fresh water this is sixty-two and a half pounds. Salt water weighs slightly more. So, all one has to do to find the pressure due to the water at any depth is to multiply the depth in feet by sixtytwo and a half, and the answer is apparent at once in pounds, says Laurence Hodges in the " Sunday Magazine" of New York.

While on the subject of increasing water pressure a number of interesting observations can be made in connection with air compressibility. Air is very,'"compressible, the volume decreasing as the pressure increases. Ef a bottle is tightly corked it will contain air at ordinary pressure of fifteen pounds to the square inch, and that is the pressure it exerts. Then tie a weight to the bottle vnd let it down in the sea by means of a string. On bringing it to the top again it will be found that the stopper has been forced into the bottle by the water pressure. If the bottle is filled with water and stoppered and let down, no such thing takes place, showing that water is not compressible to any great extent.

If by any means some air could be placed at the bottom of a sea five miles deep it would not rise to the top ; for it would Vie denser —that is, would weigh more to the cubic foot than water —and the water would have to float on the air. Hence no man knows if the bottom of .our seas is wet or not.

There is only one thing that. would prevent the air from becoming this dense, and that is if it was cold enough it would liquefy. However, it is almost inTpossible— is in fact impossible—for anything at the bottom of the sea to be colder than four degrees centigrade ; for if it got colder the water around it uould become colder and larger, and consequently lighter, and rise, and Its place would be taken hy four-degree water which would bring the object to that temperature. So we have no argument against the suggestion, for the temperature at or below which air liquefies is between one hundred and tw>o hundred degrees below zero centigrade.

Another interesting consideration along this line is why a sailor drowned in deep water rises after a time ; but a stone thrown in sinks and never rises. The body of the Bailor is subject to decomposition, which causes gases to form and the body to swell. If the body swells, we have the same weight taking up a larger volume ; consequently the body is lighter per unit volume than before, and so rises in water.

Some people seem, to think that a stone thrown into the sea can sink only to a certain depth and is there held suspended on account of the pressure of water. A body immersed in fluid is buoyed up only by the,weight of the fluid displaced. We have found that water is practically incompressible ; so if the stone diswater weighs the same or practiplaces a cubic foot of water, that cally so at the top or at the bottom of the sea. So the stone would bebuoyed up only by its weight. Thus the difference in the forces would, be always downward, and the stone would sink to the bottom.

In fact, if the stone is at all compressible, the tendency is for it to get heavier per unit volume as it goes down ; for we have the same weight in a smaller space.— "Weekly Telegraph."