"But gunnery is ballistics," the old man said. "And ballistics is
trigonometry. Big gun is fired by figuring, not by looking."

"I'm only afraid," the lad replied, "that I'll never have a chance at
the big gun. Everywhere I go, it's nothing but figuring. And I simply
can't get figures into my head."

"You really want to learn?"

"You bet I do," said Eric. "I'm working like a tinker at the stuff every
chance I get, but I don't seem to get the hang of it somehow."

"If you come to me, I teach you."

"Teach me all I want to know?" said the boy in amazement.

The old man shook his head.

"Teach you to want to know all you have to know. Teach you to like
figures."

Eric looked at him a minute.

"All right, Dan," he said, "I'll go you. I've still got some of the
money I saved up from my work this summer and I was going to spend part
of it on tutoring this winter, anyway. I'll tutor under you, whenever
I'm off duty, and if you can teach me to like figures, you're a good
one. Any way, your cottage is so near that I can get right on the job if
the station calls."

True to his word, a few days later Eric appeared at the tiny little
cottage--it was scarcely more than a hut--which was the home of the
eccentric old puzzle-maker. The top part of it was a home-made
observatory, and the whole building looked a good deal like a large
beehive.

"String in the corner," said the old man, after welcoming him. "Get
him."

"It's all knotted, Dan," the boy replied, holding up a piece of rope
with a couple of dozen strings hanging from it, of various colors, all
intertwined.

"Of course he is," the old man replied. "Read him."

"What?" asked the boy.

"Read him," repeated the old man.

"What does it mean?"

"He's what Incas used to count treasure with," the old man said. "He's
quipu, a copy of one Cortez found in City of Sun. You like to read what
he says?"

"You bet I would."

"Bring him here."

Wondering a good deal at the odd puzzle-maker's manner, for the lad had
gone to the cottage in good faith with his books, expecting to work on
the problems that were disturbing him, he brought over the knotted
quipu.

"Green string means corn," said the puzzle-maker, "because he's the
color of growing corn. What you suppose white is?"

"Silver," guessed the boy.

"Right. And yellow?"

"Gold."

"Right, too. And red?"

"Copper?" hazarded the boy.

"Not bad guess," the old man said. "Not copper color, red."

"Red