Instantly both little fellows were at Nat’s heels, through the back hall to the cellar-way, where Nat stopped to don his overalls, for he always insisted that the first principle of true mechanics was “good, stout overalls.”

Nor were the clothes protectors unbecoming to Nat.  In fact, he looked the ideal workman, except he was not exactly of the muscular build, being decidedly tall, and having such a crop of light, bushy hair.

“I’ll show you how to make gas,” said Nat as his two young cousins waited impatiently to hear the program announced.  “We can produce a very superior article by the mere use of bark from a white birch tree, and a common clay pipe.  You cut the bark up into little pieces with a pair of scissors, fill the bowl of the pipe, and then make a cover or plug for the bowl by using clay or a mixture of salt, ashes and water.  Stick the bowl of the pipe in the stove or furnace like this,” and he opened the door of the big heater; “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.

“Yes, it’s yours truly, Nat.  And for gracious’ sake, do let me in.  What isn’t frozen is paralyzed.”

“Where in the world did you come from?” asked the astonished boy as he led the way to the side door.

“From some place too dark for the earth and too cold for—­any other place.  I think, it must have been Mars,” Tavia finished, “and Mrs. Mars forgot to light the lamps.”

“But there was no train,” remarked Nat, waiting for some one from within to open the door in answer to his hasty knock.

“As if I didn’t know that, Mr. White,” replied Tavia saucily.  “Do you suppose I am the kind of girl who rides in a dump-cart in preference to taking a red plush seat in a train?”

By this time the commotion had been heard, and the door was opened by almost the entire family.