It was a curious fact that twenty feet away from the path of the wind
scarcely a breeze could be felt, while to advance a little way into it
meant that one would at once be almost carried off his feet.
Tom tested the speed of it one day with a special anemometer, and found
that only a few hundred feet inside the zone the wind blew nearly one
hundred miles an hour.
"What is it like inside, I wonder?" asked Ned.
"It must be terrific," was his chum's opinion.
"Dare you risk it, Tom?"
"Of course. The harder it blows the better the glider works. In fact I
can't make much speed in a hundred-mile wind for with us all on board
the craft will be heavy, and you must remember that I depend on the wind
alone to give me motion."
"What do you think causes the wind to blow so peculiarly here Tom?" went
on Ned.
"Oh, it must be caused by high mountain ranges on either side, or the
effects of heat and cold, the air being evaporated over a certain area
because of great heat, say a volcano, or something like that; though I
don't know that they have volcanoes here. That creates a vacuum, and
other air rushes in to fill the vacant space. That's all wind is,
anyhow, air rushing in to fill a vacuum, or low pressure zone, for you
remember that nature abhors a vacuum."
It took nearly a week to assemble the Vulture, as Tom had named his
latest craft, from the fact that it could hover in the air motionless,
like that great bird.
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