asked Tom.

"I can't explain that to you," said Sam, "because you haven't studied
geometry."

"Oh well, tell us anyhow, if we don't understand it," said Sid
Russell, who sat with his mouth open.

"Sid wants to find out how to tell how far it is from his head to his
heels, without having to make the trip when he's tired," said Bob
Sharp, who was always poking fun at Sid's long legs.

"Well," said Sam smiling, "I know the length of that line because I
know that the square described on the hypothenuse of a right angled
triangle is equal to the sum of the squares described on the other two
sides."

"Whew! it fairly takes the breath out of a fellow to hear you rattle
that off," replied Sid.

"Come," resumed Sam, "we aren't getting on with what we undertook. Now
look and listen. Here is the line we would follow if we could go
straight from Camp Jackson to Pensacola. If we could follow it, I
would only have to guess how many miles we march each day, and mark it
down on the map. But we can't go straight, because of swamps and
creeks and canebrakes, so I must keep looking at my compass to find
out what direction we do go; then I mark on the map the route we have
followed each day, and the distance, and each night's camp gives me a
new starting point."