Take an ordinary rubber sucker, such as is used on the end of a dart,
and attach it to a string. Force this down on a piece of glass. (See
Fig. 5.) The glass can then by lifted by the pressure of the air that
holds the rubber to it.
We are indebted to a German experimental philosopher named Otto Von
Guericke for knowledge of atmospheric pressure. Guericke is
distinguished by his original discoveries of the properties of the air.
He was born at Magdeburg in Prussian Saxony, November 20, 1602. He
became interested at an early age in the politics of his city, and in
1627 was elected alderman, and in 1646 Mayor of Magdeburg. While serving
in the above capacities, he devoted his leisure to science, especially
on the creation of a vacuum and the action of bodies in a vacuum. His
first experiments were conducted with a pump on a barrel of water. After
drawing off all the water, he still found that air permeated the wood of
the barrel, so he substituted a globe of copper and pumped out air also.
He thus became the inventor of the air pump and illustrated in a simple
but effective way the force of atmospheric pressure.
[Illustration:
Fig. 6
]
By placing two hollow hemispheres of copper (see Fig. 6) together, and
exhausting the air, he found that fifteen horses pulling one way and
fifteen pulling the opposite were unable to pull the hemispheres apart.
He further demonstrated that in a vacuum all bodies fall equally fast,
that animals cannot exist therein, or, in fact, living matter. He is
also credited with being the inventor of the air balance and a type of
weather cock, called the anemoscope. He was interested also in
astronomy.
[Illustration:
Fig. 7
]