ix miles high, even if you filled it
up with cotton fluff, would weigh tons and tons!"

"Well, my boy," said the Weather Forecaster, "you're carrying on the top
of your head a column of air, not only six, but sixty miles high, yes,
and more than that! You don't notice it, of course, because you're used
to it, and your body is made to accommodate itself to that weight by
your tissues being full of air at the same pressure. Just the same, not
counting the weight which presses on your whole body, amounting to about
seventeen tons, you're carrying on your head, at this minute, a weight
of over six hundred pounds."

"Six hundred pounds! As much as if I were carrying three heavy men
sitting on my head!"

"Every bit of it, and more, under certain conditions of the atmosphere.
This depends mainly on the circulation of the winds, especially those
great movements a thousand miles in diameter known as 'lows' and 'highs'
or cyclones and anti-cyclones. In the United States, an anti-cyclone
generally means fair weather, and in an anti-cyclone the barometric
column rises. That's why a barometer helps to foretell weather some time
in advance; it responds to the vast movements of the atmosphere rather
than to local conditions.

"Of course, Anton, at sixty miles up, the air is so thin that it has
hardly any weight. Indeed, we wouldn't know there was any air at that
height but for the trail that shooting stars leave. A meteor glows
because of friction, and in a vacuum there is no friction. Therefore
there must be air at the vast heights where shooting stars are first
seen."

"Could an aeroplane get up there?"

The Forecaster shook his head.

"Never," he answered. "Even six miles up, the air would be too thin to
sustain the weight of an aeroplane unless the machine were flying at
terrific velocity, and besides, at that height, there wouldn't be enough
air for an aviator to breathe. At that, Anton, you can see for yourself
that if the air is saturated with water vapor--and the cloud-bearing
atmosphere is eight or ten miles thick--there is room for a lot of
water."

"It's evaporation that puts water into the air, isn't it, sir?" asked
Ross.

"Exactly. The sun is shining on some part of the earth all the time.
There's never a second, day or night, that water is not being evaporated
from the seas, from lakes, from rivers and from the earth itself. All
the water that is taken up must fall somewhere, and all the rain that
falls mean