Long before the Iroquois reached the spot where the derelict had been seen, the captain had ordered a watch in the crow’s-nests; and for two hours at a time a man stood in each of these elevated lookouts, searching the seas for some trace of the lost vessel. But the spot where she had been seen was reached without the discovery of a single trace of her.
The captain was not in the least disturbed. He had had no expectation of finding her so soon. Wind and wave would have carried the hulk leagues to leeward of the spot. It was up to the captain to find her. When Henry stepped into the chart-room again, he found the captain plotting on his chart the course he intended to follow in his search for the derelict.
When he noticed that Henry was watching him, the captain said: “That’s what is called a grid. You see we start here, where the derelict was known to be some days ago, and we steer a course that will enable us to view the sea over a wide area. We try to follow the course we think the derelict has taken.”
“But how could you know which way a wreck would go?” asked Henry.
“If the derelict stuck up above water much, it would go in the direction of the wind rather than the water,” said the captain. “If it is mostly submerged, it would go in the direction the water was flowing. I’m going to assume that this derelict has been driven by the wind, for we’ve had this high southwest wind for nearly a week. So we’ll cover a broad belt of sea along her supposed course.”
“But how can you tell where that course is? I should think you’d get lost in this endless wilderness of water. There are no landmarks to help you know where you are.”
“You’re wrong, young man. There’s the greatest landmark in the world, right up there.”
Henry looked overhead. “I see nothing but the sun,” he said.
“That’s all a navigator needs to see,” laughed the captain. “It’s just as I told you. As long as he can see the sun, or the stars, you can’t lose him. When he looks at either through a sextant, he can tell exactly where he is.”
“I see,” said Henry. “The sun tells you your latitude and longitude.”