Jules Verne: Twenty Thousand Leagues Under the Seas

FIRST PART CHAPTER 13: Some Figures (continued)

"I'm all ears, captain."

"When I wanted to determine what increase in weight the Nautilus needed to be given in order to submerge, I had only to take note of the proportionate reduction in volume that salt water experiences in deeper and deeper strata."

"That's obvious," I replied.

"Now then, if water isn't absolutely incompressible, at least it compresses very little. In fact, according to the most recent calculations, this reduction is only .0000436 per atmosphere, or per every thirty feet of depth. For instance, to go 1,000 meters down, I must take into account the reduction in volume that occurs under a pressure equivalent to that from a 1,000-meter column of water, in other words, under a pressure of 100 atmospheres. In this instance the reduction would be .00436. Consequently, I'd have to increase my weight from 1,507.2 metric tons to 1,513.77. So the added weight would only be 6.57 metric tons."

"That's all?"

"That's all, Professor Aronnax, and the calculation is easy to check. Now then, I have supplementary ballast tanks capable of shipping 100 metric tons of water. So I can descend to considerable depths. When I want to rise again and lie flush with the surface, all I have to do is expel that water; and if I desire that the Nautilus emerge above the waves to one-tenth of its total capacity, I empty all the ballast tanks completely."

This logic, backed up by figures, left me without a single objection.

"I accept your calculations, captain," I replied, "and I'd be ill-mannered to dispute them, since your daily experience bears them out. But at this juncture, I have a hunch that we're still left with one real difficulty."

"What's that, sir?"

"When you're at a depth of 1,000 meters, the Nautilus's plating bears a pressure of 100 atmospheres. If at this point you want to empty the supplementary ballast tanks in order to lighten your boat and rise to the surface, your pumps must overcome that pressure of 100 atmospheres, which is 100 kilograms per each square centimeter. This demands a strength--"