The screech of the buoy, recurring regularly, set their ears ringing. "We've got to choke that off!" exclaimed Spurling, finally. "We'll go crazy, sure, if we have to listen to it all night." "How'll you do it? Jam something into the mouth of the whistle?" "Might smother it that way, but I know an easier one." He pushed his handkerchief into the curved end of the intake tube just as the bellowing buoy reached its lowest point. The next time it sank there was no sound. "Can't sing out unless it fills up with air," remarked Spurling. "It's human, so far!" "Is it all right to shut the signal off altogether? Mightn't some vessel strike the shoal if she doesn't hear it?" "Not much chance of that to-night! Everything'll give Cashe's a wide berth in a norther. But I'll let it scream a few times every ten minutes. That'll be often enough to warn off any craft within hearing." [Illustration: THEY STOOD CLOSE TOGETHER ON THE CIRCULAR TOP, HOLDING ON TO THE CROSSED BAILS, WAIST-HIGH] The last red embers of the sunset died out, and from horizon to horizon the sky was ablaze with stars. Even the boys, wet, hungry, and exhausted, could not be blind to such magnificence. "Good evening to study astronomy, Perce!" "Never saw a finer! But I'd want a steadier foundation than this for my telescope." As on the previous night, the sea was aglow with phosphorescence. Every wave was crested with silver. Buoy and tugging dory kept the water alive with light as they rose and fell. Leeward the long shoal broke in glittering foam. Spurling gazed silently down into the eddying tide. "Runs fast, doesn't it?" said Percy. "Yes; it's the ebb out of Fundy. Comes piling down over Cashe's at a two-knot rate. When the flood begins it'll run just as hard the other way. That's what makes the shoal so dangerous. There's only from four to seven fathoms over the ledge at low water, and that's little enough in a storm." "Were you ever down here before?" "No; but I've heard Uncle Tom Sprowl tell about the place dozens of times. Once, in particular, he was here in a schooner, hand-lining. It was almost calm, just a light east wind blowing, when they anchored an eighth of a mile to weather of the shoal. Pretty soon the decks were alive with fish. It kept breezing on all the time, and the ledge broke higher and higher; but they were having such good luck they hated to leave. So they hung to it till it got too rough for a small boat, and the breaker was twenty or thirty feet high. There was a big cod or haddock on every line, when all of a sudden the cable parted and they began to blow down on the ledge. It took some lively work to save the schooner and themselves. They got sail on her just in time to skin by the end of the breaker. Uncle Tom's been out in some pretty bad storms, but he's always said the time he parted his cable on Cashe's was the closest shave he ever had. See that shark!"