The air-globe is a piece of apparatus for demonstrating that air has
weight. (See Fig. 3.) First, the air-globe is weighed and then the air
is pumped into it; its stop-cock is closed and the globe is reweighed.
It will be found to have gained in weight. This is conclusive that air
is matter and that it has weight.
[Illustration:
Fig. 3
]
[Illustration:
Fig. 4
]
Of great importance to us in the study is the next fact, that air exerts
pressure on everything about us and upon ourselves.