How can you ascertain that air has weight?

We can do it by the barometer and by very many experiences in daily
life. If one end of a straw be dipped into a vessel of water and the
other end be sucked, the liquid will rise to the mouth. There we see
the pressure of the outside air forces the liquid through the straw
where the air was removed by sucking.


Can you show the same by another instrument?

Yes; the common water pump demonstrates the same as the straw. A tube
is placed into the water, the air is sucked out from the tube by the
movement of the pump, and the outside air presses the water through
the tube.


What are Artesian wells?

Wells so named because they were made first at Artois, in France. They
work on the principle that every liquid seeks its level. Of the rain
which falls, a part soaks into the soil of mountains, until, coming to
a layer of rocks or clay through which it cannot pass, it will collect
and be stored up. If a hole be bored into this reservoir the water
will rise in it.


Do you know some other properties of air?