The building of the ice boat by Bert and Charley Mason interested Nan almost as much as it did the boys, and nearly every afternoon she went down to the lumber¹ yard to see how the work was getting along.  
Mr. Bobbsey had given Bert just the right kind of lumber, and had a man at the saw-mill saw the sticks and boards to a proper size. He also gave his son some ropes and a pair of old iron runners from a discarded sleigh, so that all Charley had to provide was the bed-sheet already mentioned, for a sail.
 
The two boys worked with a will, and by Thursday evening had the ice boat completed. They christened the craft the Ice Bird, and Bert insisted upon it that his father come and see her.
 
"You have certainly done very well," said Mr. Bobbsey. "This looks as if you were cut out for a builder, Bert."
 
"Well, I'd like to build big houses and ships first-rate," answered Bert.
 
The sail was rigged with the help of an old sailor who lived down by the lake shore, and on Friday afternoon Bert and Charley took a short trip. The Ice Bird behaved handsomely, much to the boys' satisfaction.
 
"She's a dandy!" cried Bert. "How she can whiz before the wind."
 
"You must take me out soon," said Nan.
 
"I will," answered Bert.
 
The chance to go out with Bert came sooner than expected. On Monday morning Mrs. Mason made up her mind to pay a distant relative a visit and asked Charley if he wished to go along. The boy wanted to see his cousins very much and said yes; and thus the ice boat was left in Bert's sole charge.
 
"I'll take you out Monday afternoon, after school," said Bert to his twin sister.
 
"Good!" cried Nan. "Let us go directly school is out, so as to have some good, long rides."
 
Four o'clock in the afternoon found them at the lake shore. It was a cloudy day with a fair breeze blowing across the lake.
 
"Now you sit right there," said Bert, as he pointed² to a seat in the back of the boat. "And hold on tight or you'll be thrown overboard."
 
Nan took the seat mentioned, and her twin brother began to hoist³ the mainsail of the Ice Bird. It ran up easily, and caught by the wind the craft began to skim over the surface of the lake like a thing of life.
 
"Oh, but this is lovely!" cried Nan gleefully. "How fast the boat spins along!"
 
"I wish there were more ice boats around," answered Bert. "We might then have a race."
 
"Oh, it is pleasure enough just to sail around," said Nan.
 
Many other boys and girls wished a ride on the ice boat, and in the end Bert carried a dozen or more across the lake and back. It was rather hard work tacking⁴ against the wind, but the old sailor had taught him how it might be done, and he got along fairly well. When the ice boat got stuck all the boys and girls got off and helped push the craft along.
 
"It is 'most supper time," said Nan, as the whistle at the saw-mill blew for six o'clock. "We'll have to go home soon, Bert."
 
"Oh, let us take one more trip," pleaded her twin brother.
 
The other boys and girls had gone and they were left alone. To please Bert, Nan consented, and their course was changed so that the Ice Bird might move down the lake instead of across.
 
It had grown dark and the stars which might have shone in the sky were hidden by heavy clouds.
 
"Not too far now, remember," said Nan.
 
The wind had veered⁵ around and was blowing directly down the lake, so, almost before they knew it, the Ice Bird was flying along at a tremendous rate of speed. Nan had to hold on tight for fear of falling off, and had to hold her hat, too, for fear that would be blown away.
 
"Oh, Bert, this is too fast!" she gasped⁶, catching⁷ her breath.
 
"It's just glorious, Nan!" he cried. "Just hold on, it won't hurt you."
 
"But—but how are we to get back?"
 
Bert had not thought of that, and at the question his face fell a little.
 
"Oh, we'll get back somehow," he said evasively.
 
"You had better turn around now."
 
"Let us go just a little bit further, Nan," he pleaded.
 
When at last he started to turn back he found himself unable to do so. The wind was blowing fiercely and the Ice Bird swept on before it in spite of all he could do.
 
"Bert! Bert! Oh, why don't you turn around?&quo............