Jules Verne
20,000 Leagues Under the Sea (1869)

from Chapter IV

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"Well, Ned, I repeat it with a conviction resting on the logic of facts. I believe in the existence of a mammal power fully organised, belonging to the branch of vertebrata, like the whales, the cachalots, or the dolphins, and furnished with a horn of defence of great penetrating power."

"Hum!" said the harpooner, shaking his head with the air of a man who would not be convinced.

"Notice one thing, my worthy Canadian," I resumed. "If such an animal is in existence, if it inhabits the depths of the ocean, if it frequents the strata lying miles below the surface of the water, it must necessarily possess an organisation the strength of which would defy all comparison."

"And why this powerful organisation?" demanded Ned.

"Because it requires incalculable strength to keep one's self in these strata and resist their pressure. Listen to me. Let us admit that the pressure of the atmosphere is represented by the weight of a column of water thirty-two feet high. In reality the column of water would be shorter, as we are speaking of sea water, the density of which is greater than that of fresh water. Very well, when you dive, Ned, as many times 32 feet of water as there are above you, so many times does your body bear a pressure equal to that of the atmosphere, that is to say, 15 lb. for each square inch of its surface. It follows, then, that at 320 feet this pressure equals that of 10 atmospheres, of 100 atmospheres at 3,200 feet, and of 1,000 atmospheres at 32,000 feet, that is, about 6 miles; which is equivalent to saying that if you could attain this depth in the ocean, each square three-eighths of an inch of the surface of your body would bear a pressure of 5,600 lb. Ah! my brave Ned, do you know how many square inches you carry on the surface of your body?"

"I have no idea, Mr. Aronnax."

"About 6,500; and as in reality the atmospheric pressure is about 15 lb. to the square inch, your 6,500 square inches bear at this moment a pressure of 97,500 lb."

"Without my perceiving it?"

"Without your perceiving it. And if you are not crushed by such a pressure, it is because the air penetrates the interior of your body with equal pressure. Hence perfect equilibrium between the interior and exterior pressure, which thus neutralise each other, and which allows you to bear it without inconvenience. But in the water it is another thing."

"Yes, I understand," replied Ned, becoming more attentive; "because the water surrounds me, but does not penetrate."

"Precisely, Ned: so that at 32 feet beneath the surface of the sea you would undergo a pressure of 97,500 lb.; at 320 feet, ten times that pressure; at 3,200 feet, a hundred times that pressure; lastly, at 32,000 feet, a thousand times that pressure would be 97,500,000 lb.--that is to say, that you would be flattened as if you had been drawn from the plates of a hydraulic machine!"

"The devil!" exclaimed Ned.

"Very well, my worthy harpooner, if some vertebrate, several hundred yards long, and large in proportion, can maintain itself in such depths--of those whose surface is represented by millions of square inches, that is by tens of millions of pounds, we must estimate the pressure they undergo. Consider, then, what must be the resistance of their bony structure, and the strength of their organisation to withstand such pressure!"

"Why!" exclaimed Ned Land, "they must be made of iron plates eight inches thick, like the armoured frigates."

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