man-o'-war's man dreads.

"Dive thirty," ordered the captain, at the same time giving his wheel a
twist to direct the vessel's course according to the pointing finger of
the compass.

"Dive thirty, sir," repeated the steersman below, and with a slight
twist of his gear the horizontal rudders turned and the submarine
inclined downward; the level-indicator showed a slight slant and the
depth-gauge hand turned slowly round--twenty-two, twenty-five,
twenty-eight, then thirty feet, when the helmsman turned his wheel back
a little and the vessel forged ahead on a level keel.

At thirty feet below the surface the little craft, built like a cigar
on purpose to stand a tremendous squeeze, was subjected to a pressure of
2,160 pounds to the square foot. To realise this pressure it will be
necessary to think of a slab of iron a foot square and weighing 2,160
pounds pressing on every foot of the outer surface of the craft. Of
course, the squeeze is exerted on all sides of the submarine boats when
fully submerged, just as every one is subjected to an atmospheric
pressure of fifteen pounds to the square inch on every inch of his body.

The _Fulton_ and other submarine boats are so strongly built and
thoroughly braced that they could stand an even greater pressure without
damage.

When the commander of the _Fulton_ ordered his vessel to the surface,
the diving-steersman simply reversed his rudders so that they turned
upward, and the propeller, aided by the natural buoyancy of the boat,
simply pushed her to the surface. The Holland boats have a reserve