a solid piece of iron, but is hollow, and
so increased in bulk; for that reason the weight of the vessel and its
contents is less than that of an equal bulk of water.

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?

It is the most necessary substance for our life; it is the vehicle of
all odors and smells; it is the medium of all sounds, and brings to
our ear and so to our mind an immense knowledge of the outside world;
it is the cause of the beauty of the blue firmament or sky, of the
aurora and twilight; it is the great nurse of the whole vegetable
kingdom by clouds, rain, and dew.

What is an Aneroid Barometer?

It is a barometer in the construction of which no quicksilver or other
liquid is used. It consists of a metal box, exhausted of air, the top
of which is of thin metal, so elastic that it readily yields to
alterations in the pressure of the atmosphere. When the pressure
increases, the top is pressed inwards; when, on the contrary, it
decreases, the elasticity of the lid, aided by a spring, tends to move
it in the opposite direction. These motions are transmitted by
delicate levers to an index which moves on a scale. This barometer has
the advantage of being portable.

What is the Ear-trumpet?

A trumpet-like instrument used to aid deaf persons in hearing. Its
form is conical, and the larger end is of a bell shape; the small end
is placed in the ear, and the person talks in the large end. It ac