from .7 to .8 that of water. The first is not less than two inches
and a half thick and weighs 394 tons. The second envelope, the keel,
twenty inches high and ten thick, weighs only sixty-two tons.
The engine, the ballast, the several accessories and apparatus
appendages, the partitions and bulkheads, weigh 961.62 tons.
Do you follow all this?"

"I do."

"Then, when the Nautilus is afloat under these circumstances,
one-tenth is out of the water. Now, if I have made reservoirs
of a size equal to this tenth, or capable of holding 150 tons,
and if I fill them with water, the boat, weighing then 1,507 tons,
will be completely immersed. That would happen, Professor.
These reservoirs are in the lower part of the Nautilus.
I turn on taps and they fill, and the vessel sinks that had just
been level with the surface."

"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."

"Bravo, Captain! But how can the steersman follow the route
in the middle of the waters?"

"The steersman is placed in a glazed box, that is raised about the hull
of the Nautilus, and furnished with lenses."



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