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joined by T-shaped irons, which render it very strong. Indeed, owing to
this cellular arrangement it resists like a block, as if it were solid.
Its sides cannot yield; it coheres spontaneously, and not by the closeness
of its rivets; and its perfect union of the materials enables it to defy
the roughest seas.
"These two hulls are composed of steel plates, whose density is
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.
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