While the boys were at their noonday lunch Buck appeared to report progress. The big wagon was to come from a sheep ranch, ten miles to the south. A man had gone for it and would arrive with it that night. The wheels of the smaller wagon were being soaked in water and the axles had been greased.

Ned could not resist asking:

"How's your new boarder, Buck?"

"Ain't seen much o' him. Purty poor feeder fur a tramp. Can't get a tortilla down him nohow."

Ned looked at Alan significantly.

"Hasn't any baggage, has he?" continued Ned.

"Not a st.i.tch. Lessen you allow fur a extra suit o' underclothes."

"Under clothing?" exclaimed Ned. "Two suits?"

"Yep. And fine, too. My old woman washed a suit to-day and she 'lows as how it cost more than the rest o' his outfit."

"Don't you think that funny?"

"'What?" responded Alan sleepily.

"Why, a tramp with two suits of fine underwear?"

"Probably he stole them."

"And probably be didn't. A real tramp might steal them, but he wouldn't wear them."

"Well, what do you care," laughed Alan, "whether he's a tramp or not so long as he's useful?"

Ned was silent a few moments.

"Tramp or not, that fellow will bear watching."

"All right," conceded Alan, "I guess we can do that."

By night the barn and horse yard of the corral looked like a combination manufactory and hardware store. The seven sections of the skeleton-like car stretched across the old horse yard like a disjointed snake; crated aeroplane guides, and the propeller and the rudder leaned against the fence, looking like the frame work of a house; the more compact engine, motor, radiator and fan stood ready for unpacking under the shelter shed, while shafts, connections and boxes of small parts filled a large part of the empty stalls. The tins of gasoline for experimental flights and the first trip to Elmer's camp were in a far corner of the yard, and in the wagon shed stood the two immense special trunks containing the gas bag and the Italian hemp netting.

The evening meal was not as cheery and chatty an affair as the preceding ones had been, although Elmer had done his best in honor of their farewell. And the boys insisted that at this last meal the waiter should be dispensed with, and Elmer was put at the head of the table.

"Yo' make me feel as if I was a startin' fo' do norf pole,"

exclaimed Elmer. "I don't see what's de use of so much fussin'."

"Well, anyway," exclaimed Ned, holding up a gla.s.s of iced tea, "here's luck to you, Elmer."

"And de same to you," answered Elmer. "And to all of us."

Rising bell was to ring at four o'clock the next morning; so the boys all turned in at once after they had cleaned up the kitchen.

It was about twelve o'clock when a sudden call sounded through the car.

"Alan!".

It was Ned, who, clad in pajamas, was shaking his chum. The latter, dazed for a moment, sprang upright, soundly whacking his head on the upper berth, in which Elmer was snoring loudly.

"What is it?" he exclaimed, rolling out on the floor. "Who hit me?

Indians?"

"Not yet," laughed Ned, shaking his "pal" into wakefulness.

"Listen!"

He struck a match, lit a candle and sat down on the edge of the berth.

"You're a b.u.m calculator," he began, eyeing Alan.

"I didn't calculate where that berth was," answered Alan ruefully, rubbing a lump on the top of his head.

"And you didn't calculate where we are now," somewhat excitedly added Ned. "And I didn't think of it until just now."

"Go on," interrupted the still sleepy Alan. "If it's a riddle I give it up."

"I suppose you know what the air pressure is to a square inch,"

answered Ned, like a school teacher rebuking a slow scholar.

"Why, 14.7 pounds, of course."

"Where?" exclaimed Ned again, sharply.

"Where?" echoed Alan.

"Why, at the sea level-that's where. Not out here. Do you know how high we are above sea level right here?"

Alan began to see the point and a smile came over his face. He had no chance to answer:

"We're a little short of seven thousand feet up in the air right here in Clarkeville," continued Ned in about the same tone of exultation he might have used had he found a gold mine. "Now, listen. How many cubic feet of gas does our balloon hold?"

That question was easy. The boys knew that as well as the multiplication table.

"Sixty-five thousand, four hundred and ninety-three feet."

"And how much weight is it going to carry?"

"Three thousand nine hundred and thirty-five and a half pounds."

"Exactly," went on Ned. "That's the weight we are going to carry figured at sea level. Did it ever occur to you that our sixty-five hundred feet of hydrogen can lift more way up here seven thousand feet in the air, than it can at sea level? Did it ever occur to my special engineer and calculator that as the weight and pressure of the air grows less our hydrogen will lift just that much more weight.

"By the great horn spoon!" exclaimed Alan. "Give me that candle."

In another moment he was at the drawing room table with a pencil in his hand. It did not take him long to make his calculations.