“That’s right,” agreed John, “and we don’t want to make any mistake at the very beginning of our calculations. That would throw us ’way off later on.”
“Take this stick,” suggested George, bringing up a long thin shoot he had torn from one of the nearby bushes. “Lay it flat out on the rock and in a direct line with the needle. Be sure to get it exact and if we do we can easily enough find the ‘southern extremity.’”
This was quickly done, and in a few moments the exact spot desired was located beyond the shadow of a doubt.
“Now,” exclaimed Grant, “the next thing to do is to measure off a distance due north from here.”
“Here’s your tape measure,” laughed John, offering his shoe to Grant. “That’s exactly ten inches long. I’ll take my oath to that.”
“Let’s see,” mused Grant. “We want to measure a hundred feet from here and the shoe is ten inches long. How are we going to figure that out?”
“That’s easy enough,” exclaimed John. “You do it this way: there are twelve inches in a foot, of course, and in one hundred feet there would be one hundred times twelve, or twelve hundred. Now the shoe is ten inches long, so you divide twelve hundred by ten, which is–”
“One hundred and twenty,” said Grant quickly.
“Right,” exclaimed John. “In other words, we want to measure a distance one hundred and twenty times the length of my shoe due north from here.”
“Go ahead and do it,” urged George. “I’ll do it myself.”