"Have you a long straight board?" he asked in reply.
"Plenty of them," the younger lad answered.
"Good. Well then, to-morrow morning lay that board so that its edge touches the two points where the shadow of the rope on the pole crossed the outer circle and let Dan'l whitewash a straight line joining the two points. Do the same with the second and with the inside circles."
"Yes?" queried the lad eagerly, "and then?"
"You'll have three parallel lines," the Forecaster said, "the outer one longer and the next two shorter. Bisect those lines. Do you know how to do that?"
The younger lad shook his head.
"Only by measuring with a bit of string and doubling the string," he said.
The Forecaster took a pencil and an envelope out of his pocket.
"It's quite simple," he explained. "Fasten a string to the peg at one end of the line you want to divide in half. Stretch the string along the line till you come to the end of this line. Then make a circle. Do the same thing from the other end of the line. That will give you two circles crossing one another. With the board, draw a straight line joining the points where the circles cross.
"To be exact, bisect the line on the middle and on the inner circles in the same way. You'll find they all come out the same. The bisecting line, reaching from the pole, and crossing the bisected lines is called the plane of the meridian. If I were you, I'd make that line a permanent mark by pressing into the ground a row of stones, or those white clay marbles. Then the rain can destroy the other whitewash lines, without doing any harm, because you've got what you were after."