filled, and the boat sinks to a level with the surface of

the water.

"Very good, captain, but now we have arrived at the real difficulty. I can understand that you can get level with the surface. But in going lower down in your submarine vessel, do you not encounter a pressure, and consequently endure a pressure, from below, which may be estimated at an atmosphere for thirty feet of water, or about 15 lbs. for every square inch?"

"Quite so."

"Then unless you fill up the Nautilus altogether, I do not see how you can get her down to the bottom of the sea."

"Monsieur," replied Captain Nemo, "you cannot confuse statics and dynamics without running the risk of grave errors. It gives me very little trouble to reach the depths of the ocean, for all bodies have a tendency to sink. Do you follow me?"

"I am listening, captain."

"When I wish to determine what increase of weight I must give the Nautilus to sink her, I have only to think of the reduction in the volume of sea water, according as we get lower and lower down."

"That is clear enough," I replied.

“Now, if water be not absolutely incompressible, it is nearly so. In fact, according to the latest calculations, it is only ·000436 per atmosphere for each thirty feet of depth. If I want to descend 1,000 yards, I calculate the reduction of volume of a column of water of 1,000 yards—that is to say, under the pressure of 100 atmospheres. This reduction will then be 436 hundred-millionths. I must then increase the weight