“Well, Captain, but now we come to the real difficulty. I can understand your rising to the surface; but, diving below the surface, does not your submarine contrivance encounter a pressure, and consequently undergo an upward thrust of one atmosphere for every thirty feet of water, just about fifteen pounds per square inch?”

“Just so, sir.”

“Then, unless you quite fill the Nautilus, I do not see how you can draw it down to those depths.”

“Professor, you must not confound statics with dynamics or you will be exposed to grave errors. There is very little labour spent in attaining the lower regions of the ocean, for all bodies have a tendency to sink. When I wanted to find out the necessary increase of weight required to sink the Nautilus, I had only to calculate the reduction of volume that sea-water acquires according to the depth.”

“That is evident.”

“Now, if water is not absolutely incompressible, it is at least capable of very slight compression. Indeed, after the most recent calculations this reduction is only .000436 of an atmosphere for each thirty feet of depth. If we want to sink 3,000 feet, I should keep account of the reduction of bulk under a pressure equal to that of a column of water of a thousand feet. The calculation is easily verified. Now, I have supplementary reservoirs capable of holding a hundred tons. Therefore I can sink to a considerable depth. When I wish to rise to the level of the sea, I only let off the water, and empty all the reservoirs if I want the Nautilus to emerge from the tenth part of her total capacity.”

I had nothing to object to these reasonings.

“I admit your calculations, Captain,” I replied; “I should be wrong to dispute them since daily experience confirms them; but I foresee a real difficulty in the way.”

“What, sir?”

“When you are about 1,000 feet deep, the walls of the Nautilus bear a pressure of 100 atmospheres. If, then, just now you were to empty the supplementary reservoirs, to lighten the vessel, and to go up to the surface, the pumps must overcome the pressure of 100 atmospheres, which is 1,500 lbs. per square inch. From that a power——”

“That electricity alone can give,” said the Captain, hastily. “I repeat, sir, that the dynamic power of my engines is almost infinite. The pumps of the Nautilus have an enormous power, as you must have observed when their jets of water burst like a torrent upon the Abraham Lincoln. Besides, I use subsidiary reservoirs only to attain a mean depth of 750 to 1,000 fathoms, and that with a view of managing my machines. Also, when I have a mind to visit the depths of the ocean five or six mlles below the surface, I make use of slower but not less infallible means.”

“What are they, Captain?”

“That involves my telling you how the Nautilus is worked.”

“I am impatient to learn.”

“To steer this boat to starboard or port, to turn, in a word, following a horizontal plan, I use an ordinary rudder fixed on the back of the stern-post, and with one wheel and some tackle to steer by. But I can also make the Nautilus rise and sink, and sink and rise, by a vertical movement by means of two inclined planes fastened to its sides, opposite the centre of flotation, planes that move in every direction, and that are worked by powerful levers from the interior. If the planes are kept parallel with the boat, it moves horizontally. If slanted, the Nautilus, according to this inclination, and under the influence of the screw, either sinks diagonally or rises diagonally as it suits me. And even if I wish to rise more quickly to the surface, I ship the screw, and the pressure of the water causes the Nautilus to rise vertically like a balloon filled with hydrogen.”