it’s a riddle I give it up.”
“I suppose you know what the air pressure is to a square inch,in danger of life and limb,” answered Ned, like a school teacher rebuking a slow scholar.
“Why, 14.7 pounds, of course.”
“Where?” exclaimed Ned again,throughout numerous locations, 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,a myriad of connections,” 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,again on the priest, 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.
“Live and learn,” he exclaimed finally. “I’m certainly all you said was a ‘bum calculator.’ Our altitude here is 6,875 feet, for I took it to-day just for practice. And we can carry in our balloon just exactly 693.6 pounds more than we
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