ould not be great
enough to lift it so high, no matter how hard you sucked,--that is, no
matter how perfect a vacuum you made in the upper part of the straw.
The lemonade would rise part way, and then your straw would be
flattened by the pressure outside.

Some days the air can force water up farther in a tube than it can
on other days. If it can force the water up 33 feet today, it will
perhaps be able to force it up only 30 feet immediately before a
storm. And if it forces water up 33 feet at sea level, it may force it
up only 15 or 20 feet on a high mountain, for on a mountain there
is much less air above to make pressure. The pressure of the air is
different in different places; where the air is heavy and pressing
hard, we say the pressure is _high_; where the air is light and not
pressing so hard, we call the pressure _low_. A place where the air is
heavy is called an area of high pressure; where it is light, an area
of low pressure. (See Section 44.)

WHAT MAKES WINDS? It is because the air does not press equally all
the time and everywhere that we have winds. Naturally, if the air is
pressing harder in one place than in another, the lower air will be
pushed sidewise in the areas of high pressure and will rush to the
areas where there is less pressure. And air rushing from one place to
another is called _wind_.

[Illustration: FIG. 10.]

_APPLICATION 4._ A man had two water reservoirs, which stood
at the same level, one on each side of a hill. The hill
between them was about 50 feet high. One reservoir was full,
and the other was empty. He wanted to get some of the water
from the full reservoir into the empty one. He did not have a
pump to force the water from one to the other, but he did have
a long hose, and could have bought more. His hose was long
enough to reach over the top of the hill, but not long enough
to go around it. Could he have siphoned the water from one
reservoir to the other? Would he have had to buy more hose?

_APPLICATION 5._ Two boys were out hiking and were very
thirsty. They came to a deserted farm and found a deep well;
it was about 40 feet down to the water. They had no pump,
but there was a piece of hose about 50 feet long. One boy
suggested that they drop one end of the hose down to the water
and suck the water up, but the other said that that would not
work--the only way would be to lower the hose into the water