"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.
"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.
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