“That question deserves an answer,” Captain Nemo replied. “First off, I’ll mention that at the bottom of the sea there exist veins of zinc, iron, silver, and gold whose mining would quite certainly be feasible. But I’ve tapped none of these land-based metals, and I wanted to make demands only on the sea itself for the sources of my electricity.” “The sea itself?” “Yes, professor, and there was no shortage of such sources. In fact, by establishing a circuit between two wires immersed to different depths, I’d be able to obtain electricity through the diverging temperatures they experience; but I preferred to use a more practical procedure.” “And that is?” “You’re familiar with the composition of salt water. In 1,000 grams one finds 96.5% water and about 2.66% sodium chloride; then small quantities of magnesium chloride, potassium chloride, magnesium bromide, sulfate of magnesia, calcium sulfate, and calcium carbonate. Hence you observe that sodium chloride is encountered there in significant proportions. Now then, it’s this sodium that I extract from salt water and with which I compose my electric cells.” “Sodium?” “Yes, sir. Mixed with mercury, it forms an amalgam that takes the place of zinc in Bunsen cells. The mercury is never depleted. Only the sodium is consumed, and the sea itself gives me that. Beyond this, I’ll mention that sodium batteries have been found to generate the greater energy, and their electro-motor strength is twice that of zinc batteries.” “Captain, I fully understand the excellence of sodium under the conditions in which you’re placed. The sea contains it. Fine. But it still has to be produced, in short, extracted. And how do you accomplish this? Obviously your batteries could do the extracting; but if I’m not mistaken, the consumption of sodium needed by your electric equipment would be greater than the quantity you’d extract. It would come about, then, that in the process of producing your sodium, you’d use up more than you’d make!” “Accordingly, professor, I don’t extract it with batteries; quite simply, I utilize the heat of coal from the earth.” “From the earth?” I said, my voice going up on the word. “We’ll say coal from the seafloor, if you prefer,” Captain Nemo replied. “And you can mine these veins of underwater coal?” “You’ll watch me work them, Professor Aronnax. I ask only a little patience of you, since you’ll have ample time to be patient. Just remember one thing: I owe everything to the ocean; it generates electricity, and electricity gives the Nautilus heat, light, motion, and, in a word, life itself.” “But not the air you breathe?”