stands for war," said Eric meditatively, then, with an inspiration,
"in those days a country was rich if it had soldiers. Does the red mean
soldiers, Dan?"

"Soldiers, right," the old man answered. "The Quipucamayocuna--"

"The what, Dan?"

"Knot officers," explained the other, "kept track of him all. They
counted tens, single knot meant ten; double knot, hundred. Now read him.
Cross-knotting is for groups."

Eric worked for a quarter of an hour and then looked up.

"I've got it," he said.

"What is he?"

"In this town," said the boy, "there were seven regiments of soldiers,
I've got down the exact number of men in each regiment. Some had plenty
of food in the regimental storehouse, some had only a little. But--if I
get it right--there was money belonging to each regiment in a
treasure-house, somewhere, like a bank. I suppose they could exchange
this for food. And, if I've read it right, there was one regiment which
had money but no men. I suppose they were wiped out in battle."

"Very good," answered the puzzle-maker, looking pleased. "You keep
accounts, your own money?"

"Of course," answered the boy, pulling out a little diary from his
pocket.

"Here, string," said the old man. "Write your week's accounts in quipu."

Thoroughly interested, Eric took up a pile of colored strings, from the
corner and started to convert his week's accounting into quipu. He
worked for half an hour, but couldn't make it come out right. It proved
an exasperating puzzle, because it seemed impossible and yet conveyed
the suggestion that there ought to be some way of doing it. Already Eric
had so keen a sense of the old man's comments that he hated to say that
he couldn't do it. But, after a while, red in the face and quite
ashamed, he said,

"I can't do it, Dan."

"No, he is not possible," said the puzzle-maker cheerfully. "That's what
I wanted you to find. The quipu is wonderful but he's not wonderful
enough, eh?"

"We'd have trouble trying to handle a big modern banking business by it,
all right," the boy agreed. "But, Dan, how about this studying I'm
supposed to do?"

"You know Latin numerals?" the old man replied.

"Of course!" Eric answered indignantly. "I couldn't even tell the time
if I didn't!"

"Write 'Four,'" came the order.

Promptly the boy wrote "IV."

"Now look at watch."

"It's got four ones there," Eric said ruefully.

"The 'IV' form is late," said the puzzle-maker. "I show you something.
Copy c