EXTRAOEDINARY SHIPS. 
13 
is fastened to tlie great sea-castle^s keel_, tlie fine copper wires 
are carefully nncoiled_, the submarine fiend -ship sinks down 
again^ gently screws back a short distance out of danger. The 
subtle battery is connected with the wires^ and the great roar 
of the explosion but dimly reverberates through those silent 
depths; the splash of the hundreds of mangled bodies is 
neither heard nor seen. How will this submarine monster 
rise or sink after her first delicate adjustment to the slightly 
denser water to which she has gone down ? How can her sailors 
continue to live and breathe in the impure closed up hull ? Yery 
well indeed. Hid you ever try to compress water ? You 
could not do it. Of the greatest volume you ever tried you 
could not get a perceptible compression. But you can com- 
press air. You have used it in your air-gun. Well^ you can 
compress air to the pressure of 5001b. to the square inch; it 
has been compressed more than this_, a great deal more. Now^ 
air at 500 lb. pressure to the inch is air at the pressure of 
more than thirty-three atmospheres ; that is to say^ every cubic 
foot of this compressed air will expand when let out into 
nearly 34 cubic feet. So the air in a cabin 10 feet square 
could be entirely replaced thirty-three times by a thousand 
cubic feet of compressed air at this pressure. The compressed 
air then is taken down in the submarine vessel in pipes_, and 
let out by valves as required. 
The life of the men can be supported^ and the weight of the 
vessel adjusted to the density by the water around her^ as 
long as a single foot of compressed air remains. When her 
stock is nearly exhausted she would be brought of course to 
the surface — her engines would be worked to condense more 
air — and having taken fresh breath she might take other under- 
water excursions^ until her captain put an end to her voyages^ 
as we intend now to do to this chapter. 
EXPLANATION OF PLATE I. 
Fig. 1. — The “Cigar-ship.” a b, the end cones; c d, the raised deck; ef, 
the screw-propellers. 
Fig. 2. — The “ Connector-ship.” 
