"the fire causes the birchbark to give off a gas, it comes up into the
pipestem, and can be lighted at the end, thus--"

"What was that?" interrupted Joe. "A wagon outside?"

"Might be," admitted Nat, "but what's that got to do with making birchbark
gas?"

"I thought I heard some one call," apologized Joe, again taking his place
in front of the heater.

"There is some one calling," declared little Roger. "I just heard them."

"Well, I guess we had better give up the gas business," said Nat
impatiently, "and you kids might as well go out and interview the night
air." And with this he threw down the long-stemmed pipe, which broke into
a dozen pieces. Then, while the younger boys made their way back to the
kitchen, Nat started for the yard.

"My, it's cold!" he could not help exclaiming as he stepped out into the
clear, frosty air.

Then he brushed against something.

"It's a wonder you wouldn't knock me down!" came a voice, struggling
between cold and laughter.

"Tavia!" he gasped, recognizing the tones in spite of the chattering teeth
and the forced laughter.