"That's so; but how's the old sycamore to help us?"
"By giving us a point to take sight from. Let me show you. Our proper course of march is in the direction of a line drawn from the sycamore to this pine tree. What we want to do is to prolong that line, and find some tree further on that stands in it. If I stand on the line, between the sycamore and the pine and turn my face toward the pine, I'll be looking in exactly the right direction, and can pick out the right tree to march to, by sighting on the pine. The trouble is to get in the right place to take sight from. To do that I must find the line between the sycamore and the pine. Now you go over there beyond the pine, and take sight on it at the sycamore till you get the two trees in a line with you. Then I'll stand over here, between the two object trees, and move to the right or left as you tell me to do, till you find that I am exactly in the line between them. Then I can pick out the right tree ahead."
Sid did as he was told, the boys all looking on with great interest, and presently Sam had selected their next object tree. The boys were astonished greatly at what they thought Sam's marvellous knowledge, but to their wondering comments Sam replied:—
"I haven't done anything wonderful. A little knowledge of mathematics has helped me, perhaps, but there isn't a thing in all this that isn't perfectly simple. Any one of you might have found out all this for himself, without books and without a teacher. It only requires you to think a little and to use your eyes. Besides you've all done the same thing many a time."
"I'll bet I never did," said Billy Bowlegs.
"Yes you have, Billy, but you did it without thinking about it."
"When?"
"Whenever you have shot a rifle at anything."
"How?"
"By taking aim. You look through one sight over the other and at the game, and you know then that you've got it in a line with your eye and the sights. I've only been turning the thing around, and nobody taught me how. You've only got to use your eyes and your head to make them worth ten times as much to you as they are now."