Captain Nemo decided to make for the ocean floor by submerging on an appropriately gradual diagonal with the help of his side fins, which were set at a 45 degrees angle to the Nautilus's waterline. Then the propeller was brought to its maximum speed, and its four blades churned the waves with indescribable violence.

Under this powerful thrust the Nautilus's hull quivered like a resonating chord, and the ship sank steadily under the waters. Stationed in the lounge, the captain and I watched the needle swerving swiftly over the pressure gauge. Soon we had gone below the livable zone where most fish reside. Some of these animals can thrive only at the surface of seas or rivers, but a minority can dwell at fairly great depths. Among the latter I observed a species of dogfish called the cow shark that's equipped with six respiratory slits, the telescope fish with its enormous eyes, the armored gurnard with gray thoracic fins plus black pectoral fins and a breastplate protected by pale red slabs of bone, then finally the grenadier, living at a depth of 1,200 meters, by that point tolerating a pressure of 120 atmospheres.

I asked Captain Nemo if he had observed any fish at more considerable depths.

"Fish? Rarely!" he answered me. "But given the current state of marine science, who are we to presume, what do we really know of these depths?"

"Just this, captain. In going toward the ocean's lower strata, we know that vegetable life disappears more quickly than animal life. We know that moving creatures can still be encountered where water plants no longer grow. We know that oysters and pilgrim scallops live in 2,000 meters of water, and that Admiral McClintock, England's hero of the polar seas, pulled in a live sea star from a depth of 2,500 meters. We know that the crew of the Royal Navy's Bulldog fished up a starfish from 2,620 fathoms, hence from a depth of more than one vertical league. Would you still say, Captain Nemo, that we really know nothing?"

"No, professor," the captain replied, "I wouldn't be so discourteous. Yet I'll ask you to explain how these creatures can live at such depths?"

"I explain it on two grounds," I replied. "In the first place, because vertical currents, which are caused by differences in the water's salinity and density, can produce enough motion to sustain the rudimentary lifestyles of sea lilies and starfish."

"True," the captain put in.

"In the second place, because oxygen is the basis of life, and we know that the amount of oxygen dissolved in salt water increases rather than decreases with depth, that the pressure in these lower strata helps to concentrate their oxygen content."

"Oho! We know that, do we?" Captain Nemo replied in a tone of mild surprise. "Well, professor, we have good reason to know it because it's the truth. I might add, in fact, that the air bladders of fish contain more nitrogen than oxygen when these animals are caught at the surface of the water, and conversely, more oxygen than nitrogen when they're pulled up from the lower depths. Which bears out your formulation. But let's continue our observations."

My eyes flew back to the pressure gauge. The instrument indicated a depth of 6,000 meters. Our submergence had been going on for an hour. The Nautilus slid downward on its slanting fins, still sinking. These deserted waters were wonderfully clear, with a transparency impossible to convey. An hour later we were at 13,000 meters-- about three and a quarter vertical leagues--and the ocean floor was nowhere in sight.

However, at 14,000 meters I saw blackish peaks rising in the midst of the waters. But these summits could have belonged to mountains as high or even higher than the Himalayas or Mt. Blanc, and the extent of these depths remained incalculable.

Despite the powerful pressures it was undergoing, the Nautilus sank still deeper. I could feel its sheet-iron plates trembling down to their riveted joins; metal bars arched; bulkheads groaned; the lounge windows seemed to be warping inward under the water's pressure. And this whole sturdy mechanism would surely have given way, if, as its captain had said, it weren't capable of resisting like a solid block.