it is warm
than when it is cold."

"Is that why muggy days are so uncomfortable?" asked Ross.

"Yes. When the air is full of water vapor, it hasn't the same readiness
to absorb it. When you perspire on a dry, hot, windy day, the air
absorbs it right away, but on a day that's humid or muggy, the air can't
hold any more, so it doesn't evaporate and the perspiration trickles
down your back and into your eyes. A moist climate feels hotter in the
summer and colder in the winter than a dry one, although, in reality, it
isn't as hot or as cold. Every moist climate is a cloudy climate, and
Ireland--which is called the Green or Emerald Isle because there's so
much rain that none of the vegetation ever dries up--has some of the
most beautiful clouds in the world."

"Is there any place in the United States without clouds?" asked Ralph.

"There's no place in the world that's absolutely cloudless," was the
answer, "but clouds in some deserts are few and far between. There's one
well known hotel, in the Southwest, that advertises 'free board every
day that the sun doesn't shine.' It's a safe offer, too, for last year
they only lost two days on it. There are some clouds there, but not such
as to obscure the sun.

"In a cloudless country, boys, there are great extremes of temperature,
as much as forty to fifty degrees between noon and midnight. You'll get
sunstroke in the early part of the afternoon and shiver under blankets
in the evening. That's because there are no protecting layers of clouds
to equalize the radiation. The air, especially high up, is very cold.
Don't forget that the upper clouds are all made of ice crystals."

"I've been wondering," said Anton, "how you can find out that it's so
cold high up in the air if no one can live up there?"

"Balloonists have often passed through clouds of ice crystals and snow,"
the Forecaster answered, "though, of course, they've not been as high as
the upper clouds. Many observations have been made by releasing small
sounding balloons with an instrument attached, letting them go as high
as they could, until they burst and fell to the ground. But much of our
upper-air exploring has also been done with kites."

"Kites? Like Franklin's?"

"Not quite," said the Forecaster; "our weather kites aren't built like
that. They look more like a box. I'm expecting one here, every day."

"Here?"

"Yes, boys," the Forecaster answered, "right here. There's a young chap
I know who used to wor