"Then suddenly the fog-horn sounded again, not four lengths away, sir, and the queer thing is it had been sounding the whole blamed time—we got positive proof of it afterward—only we hadn't heard it. The explanation was that we had passed through two sound zones—that's what the scientific people call 'em—and I can tell you those sound zones make considerable trouble for pilots."
To this perplexing statement the others nodded grave assent, and Breed capped the tale with a sound-zone story of his own. It was just off quarantine, and he was turning a liner to bring her up to dock when another liner came along, also running in. Breed gave the signal three times for the other liner to port her helm, and she signaled back three times for him to port his. By good luck each vessel did the right thing, and they passed safely, but neither pilot heard the whistle of the other, and each made angry complaint that the other had failed to whistle: yet witnesses testified that both had whistled, and each one swore that he had.
The truth was, according to the gentlemen who explain acoustic puzzles, that these two steamers happened to be placed there down the bay like two people in a whispering gallery, who cannot hear each other where they are, but would hear plainly if they moved further apart or drew closer together, so as to be in the foci of sound. Thus it was that distant vessels heard both sets of whistles, although there was a nearer region where these were inaudible.
Investigation has shown that these sound zones frequently establish themselves at sea (they vary in extent with wind and tide), so that the sound of horn or bell may be heard for a mile or two, and then become inaudible for, say, two miles, and then become audible again, almost as plainly as at first, for several miles more. The theory is that the sound-waves somehow go skipping over the sea, like a flat pebble over a mill-pond, in long jumps, and that a vessel under the highest part of one of these jumps is out of the sound influence, but will come into it again by going ahead a certain distance or going back a certain distance. Whether this explanation be the true one or not, the facts are abundantly vouched for, and are believed to explain various collisions and wrecks that have long been looked upon as mysteries.
"There are lots of queer things about our business," reflected an old pilot. "Now, you take steamers, they're just as different as people; each one has her own ways, and most likely her own partic'lar kind of crankiness. They talk about twin steamers, but there's no such thing. You can have 'em both made in the same yard, with every measurement alike, and they'll be as different, sir, as—as two violins. Why, I never saw a craft that'd sail the same on both tacks; they're always harder on one than the other. And as for compasses—well, I don't suppose there's ever two that came into this port with needles pointing just the same way. They all lean a shade one way or the other, same as watches."
"Lean a shade!" put in another man. "I've known 'em to lean a whole lot. I've known a steamer's compass to point plumb northeast instead of north. And that time we nearly went on the rocks by it. We were coming along past Fire Island, and the night was pretty thick. I felt something was queer and wouldn't go below, although the captain wanted me to. I kept looking up, looking up, searching for the north star, and pretty soon I made it out, or thought I did, through a rift in the blackness.
"'Hold on!' said I to the captain, 'something's the matter with your compass. There's the north star ahead of us, and it ought to be abaft the bridge.'
"'North star nothing,' said the captain. 'You're tired, man; you need a rest. Now, you just turn in for an hour, and I'll run her.'
"'You'll run her on the rocks,' said I, 'inside of fifteen minutes unless you pull her out of here. I tell you that compass is crazy.'
"Well, sir, he began to get scared when he saw me so positive, and a little later he pulled her out—just in time, too, for we were right on the breakers of Long Island, thanks to that lying compass. I've heard it's the magnetic sand at Shinnecock that devils compasses. You know there's acres and acres of it along there."