'Twenty years ago--I remember it well--a boat went ashore on that very Ledge. The tide was running out--strong, like to-night. There was three men in her--visitors they were, who wanted to save the boatman's pay. Their bodies was never found.' Then both pulled on in silence, and doggedly. In ten minutes or more they had rounded the Point at a respectful distance, for reasons well known to the navigator and the nautical surveyor of Scilly. Peter, without a word, shipped his oar. Armorel did likewise. Then Peter stepped the mast and hoisted the sail, keeping the line in his own hand, and looked ahead, while Armorel took the helm. 'It's Jinkins's boat,' said Peter, because they were now in sight of her. 'What'll Jinkins say when he hears that his boat's gone to pieces?' 'And the two men? Who are they? Will Jinkins say nothing about the men?' 'Strangers they are; gentlemen, I suppose. Well, if the breeze doesn't soon---- Ah, here it is!' The wind suddenly filled the sail. The boat heeled over under the breeze, and a moment after was flying through the water straight up the broad channel between the two Minaltos and Samson. The sun was very low now. Between them and the west lay the boat they were pursuing--a small black object, with two black silhouettes of figures clear against the crimson sky. And now Armorel perceived that they had by this time gotten an inkling, at least, of their danger, for they no longer sat passive, but had torn up a plank from the bottom, with which one, kneeling in the bows, was working as with a paddle, but without science. The boat yawed this way and that, but still kept on her course drifting to the rocks. 'If she touches the Ledge, Peter,' said Armorel, 'she will be in little bits in five minutes. The water is rushing over it like a mill-stream.' This she said ignorant of mill-streams, because there are none on Scilly; but the comparison served. 'If she touches,' Peter replied, 'we may just go home again. For we shall be no good to nobody.' Beyond the boat they could plainly see the waters breaking over the Ledge; the sun lit up the white foam that leaped and flew over the black rocks just showing their teeth above the water as the tide went down. Here is a problem--you may find plenty like it in every book of algebra. Given a boat drifting upon a ledge of rocks with the current and the tide; given a boat sailing in pursuit with a fair wind aft; given also the velocity of the current and the speed of the boat and the distance of the first boat from the rocks: at what distance must the second boat commence the race in order to catch up the first before it drives upon the rocks?