,
close the upper end, pull the hose out and let the water pour
out of the lower end of the hose into their mouths. A stranger
came past while the boys were arguing, and said that neither
way would work; that although the hose was long enough, the
water was too far down to be raised in either way. He advised
the boys to find a bucket and to use the hose as a rope for
lowering it. Who was right?

INFERENCE EXERCISE

EXPLANATORY NOTE. In the inference exercises in this book,
there is a group of facts for you to explain. They can always
be explained by one or more of the principles studied, like
gravitation, water seeking its own level, or air pressure. If
asked to explain why sucking through a straw makes soda water
come up into your mouth, for instance, you should not merely
say "air pressure," but should tell why you think it is air
pressure that causes the liquid to rise through the straw. The
answer should be something like this: "The soda water comes
up into your mouth because the sucking takes the air pressure
away from the top of the soda water that is in the straw. This
leaves the air pressing down only on the surface of the soda
water in the glass. Therefore, the air pressure pushes the
soda water up into the straw and into your mouth where the
pressure has been removed by sucking." Sometimes, when you
have shown that you understand the principles very well,
the teacher may let you take a short cut and just name the
principle, but this will be done only after you have proved by
a number of full answers that you thoroughly understand each
principle named.

Some of the following facts are accounted for by air pressure;
some by water seeking its own level; others by gravitation.
See if you can tell which of the three principles explains
each fact:

1. Rain falls from the clouds.

2. After rain has soaked into the sides of mountains it runs
underground and rises, at lower levels, in springs.

3. When there are no springs near, people raise the water from
underground with suction pumps.

4. As fast as the water is pumped away from around the bottom
of a pump, more water flows in to replace it.

5. After you pump water up, it flows down into your pail from
the spout of the pump.

6. You can drink lemonade through a straw.

7. If a lemon s