OCEAN PRESSURES

Evening Post, Volume CIV, Issue 104, 29 October 1927, Page 21

OCEAN PRESSURES

POPULAR BELIEFS DISPROVED.

There is a very prevalent idea that 'as one goes deep down into the oceans the water at those profound depths increases very greatly in density and takes on a consistency like treacle as a'result of the great pressure to which it is subjected. As a corollary to this belief it is of ten thought that ships and' bodies and the like do not sink to the ocean bed, but "find thier level" and' float, around that level until such time as final disintegration takes place. But there is a fallacy in this line of thought (writes William H. Pick, B.Sc, IVR.A.S., in icat "Newcastle Weekly Chronicle"). True that the pressure does very greatly increase, but the consistency of .density of the water does not. To consider these two factors in more detail:,33ft of salt water is roughly, equal, to 30in of mercury; that is to say, roughly, to one atmosphere pressure or 151b to the square inch. At 66ft down, therefore; the pressure is 301b to the square inch, excluding the pressure due to the true atmosphere outside, and at 99ft 451b to the square inch, and so on, until at a depth of 4000 fathoms (24,000 ft) the pressure would attain to 720 atmospheres, or nearly five tons, to. the square inch. Compressibility is, however, marked liy. far less. striking increase. Water is compressible only, by about one twenty-thousandth of its volume for one atmosphere of pressure, and at 4000 fathoms, 10,500 cubic feet of surface water would be compressed into the compass of 10,000 cubic feet. In other words, the density only increases a little. The idea, then, that the depths of the ocean are littered with floating ships and debris, is not justified—all such things are probably resting quietly on the bottom. A ship sinking would go on sinking until its fall was arrested by the ocean bed. Changes there would be due to implosion; that is, "explosion inwards." For example, every hermetically closed chamber- would be so imploded because the. ever-increasing pressure on the outside could not be counterbalanced on' the inside, but that would be about all — and actual, experiments done on bodies of animals by lowering them to great depths on the. end of a line reveal that these bodies, when pulled up, are little altered in appearance. Strange effects are noticed, however, in the case of fish whose natural habitation is at profound depths andv-whose bodies are, therefore, framed to withstand. tremendous pressure and to fnnction in tremendous pressure. If, through any caprice of Mother Ocean, any untoward sub-oceanic upheaval, such a fish gets elevated irom the level in which it normally has its being, the decrease of pressure experienced causes its swimming bladders to distend. This expansion means a Teduetion. in its, specific gravity; that is, of its weight per cubic volume, and. it begins to float upward. Up to a certain limit it can, by muscular reactions, counteract this upward movement. The time arrives, however, when any further muscular adjustments are inadequate. Prom that point the fish" inevitably goes upward and upward, powerless to stop the rise, tumbling to the. surface grotesquely. The pressuro on it steadily gets less and less as it tumbles onward, and, in consequence; its organs become gradually more and more distended, until so much distension is obtained that death results, death due to under-pressure and not to ever.