During this phase of our voyage, Captain Nemo conducted interesting experiments on the different temperatures in various strata of the sea. Under ordinary conditions, such readings are obtained using some pretty complicated instruments whose findings are dubious to say the least, whether they’re thermometric sounding lines, whose glass often shatters under the water’s pressure, or those devices based on the varying resistance of metals to electric currents. The results so obtained can’t be adequately double-checked. By contrast, Captain Nemo would seek the sea’s temperature by going himself into its depths, and when he placed his thermometer in contact with the various layers of liquid, he found the sought-for degree immediately and with certainty. And so, by loading up its ballast tanks, or by sinking obliquely with its slanting fins, the Nautilus successively reached depths of 3,000, 4,000, 5,000, 7,000, 9,000, and 10,000 meters, and the ultimate conclusion from these experiments was that, in all latitudes, the sea had a permanent temperature of 4.5 degrees centigrade at a depth of 1,000 meters. I watched these experiments with the most intense fascination. Captain Nemo brought a real passion to them. I often wondered why he took these observations. Were they for the benefit of his fellow man? It was unlikely, because sooner or later his work would perish with him in some unknown sea! Unless he intended the results of his experiments for me. But that meant this strange voyage of mine would come to an end, and no such end was in sight. Be that as it may, Captain Nemo also introduced me to the different data he had obtained on the relative densities of the water in our globe’s chief seas. From this news I derived some personal enlightenment having nothing to do with science. It happened the morning of January 15. The captain, with whom I was strolling on the platform, asked me if I knew how salt water differs in density from sea to sea. I said no, adding that there was a lack of rigorous scientific observations on this subject. “I’ve taken such observations,” he told me, “and I can vouch for their reliability.” “Fine,” I replied, “but the Nautilus lives in a separate world, and the secrets of its scientists don’t make their way ashore.” “You’re right, professor,” he told me after a few moments of silence. “This is a separate world. It’s as alien to the earth as the planets accompanying our globe around the sun, and we’ll never become familiar with the work of scientists on Saturn or Jupiter. But since fate has linked our two lives, I can reveal the results of my observations to you.” “I’m all attention, captain.” “You’re aware, professor, that salt water is denser than fresh water, but this density isn’t uniform. In essence, if I represent the density of fresh water by 1.000, then I find 1.028 for the waters of the Atlantic, 1.026 for the waters of the Pacific, 1.030 for the waters of the Mediterranean—”