"Then a detachable upper deck," I said, "that would stay in place by gravity, but float if the hull sank."
"It would break into pieces in a seaway. It would need to be an upper section of two decks with an air space. Well, how about hatches, stairways, and masts leading to the lower body? The two ends of the ship, which are clear of these fixtures, would not hold all hands, and if you do away with hatches, making this upper section water-tight, how about the hundreds of people—engineers, firemen, and steerage passengers—imprisoned in the hull?"
"Right," I answered. "It seems, then, that the only safety from ice is in the Southern Lane route, and slow speed in a fog."
"Yes, unless this English scientist's invention proves practicable. Have you read of it?"
I had not, and said so.
"He intends," he explained, "to send forth at intervals sharp notes of inaudible sound which, acting like audible sound, will come back from an iceberg, a ship, or a coast as an echo, and the time elapsed, recorded by a suitable receiver, and divided by two, will give the distance."
"Inaudible sound," I answered. "That seems anomalous."
"Hypothetical rather—not yet proven. But who knows? There are sounds of too low and long a vibration—I do not mean the roll of a drum, which is merely a succession of beats—that cannot be cognized by the human ear. There are sounds too high to be heard, such sounds as the chirp of a cricket, or tweet of a bird. Some people never hear these sounds. Why not use these sounds, and receive their echoes by delicate instruments?"
"Give it up," I said hopelessly.
"They call silence the negation of sound," he continued, "as they call darkness the negation of light. There is polarity throughout the universe. We are aware of plus and minus quantities in mathematics, each calculable by the same methods.