Granting that the pressure of the atmosphere may be represented by the pressure of a column of water thirty-two feet high. In reality the column of water would be of less height, since it would be sea-water, whose density is superior to that of fresh-water. Well, when you dive, Ned, so long as you have thirty-two feet of water above you your body is supporting a pressure equal to that of the atmosphere, that is to say a kilogramme for each square centimetre of surface. It follows that at 320 feet this pressure would be equal to 10 atmospheres, and to 100 atmospheres at 3,200 feet, and 1,000 atmospheres at 32,000 feet, which is about two and a half leagues. This is equivalent to saying that 1f you could reach this depth, each square centimetre of your body would bear a pressure of 1,000 kilogrammes. Now, my brave Ned, do you know how many square centimetres of surface there are in your body?”
“I cannot tell, M. Aronnax.”
“About 17,000.”
“So many as that?”
“And as, in fact, the atmospheric pressure is a little greater than one kilogramme to a square centimetre your 17,000 square centimetres are at this moment supporting a pressure of 17,568 kilogrammes (97,500 lbs.).
“Without my being sensible of it?”
“Without your being sensible of it. And, if you are not crushed by this pressure, it is because the air enters the body with an equal force. So the inward and out ward pressure are equal, and neutralise each other, and you can support it without inconvenience. But in the water it is a different thing.”
“Yes, I understand,” replied Ned, who was now
