[Illustration: FIG. 1.]
Here are two very simple experiments that will not fail to excite a good
deal of interest and wonderment among persons who are unfamiliar with
them.
The first illustrates the pressure of the atmosphere. Take a coin and
rub it against some oaken book-case or very smooth wooden surface, as
shown in Fig. 1. Press it hard for a moment, and then withdraw the
fingers. The coin will continue to stick to the wood.
The reason of this is that the rubbing and the pressure have dispersed
the air which was between the coin and the wood, and the pressure of the
atmosphere is sufficient to keep the coin in its place.
[Illustration: FIG. 2.]
To perform the experiment shown in Fig. 2 fill a glass carefully with
water up to the brim, so that the surface of the water is rounded. Then
ask the by-standers how many coins can be thrown into the glass without
the water over-flowing. Some will emphatically declare that it will not
hold one; others will admit that there may possibly be room for one or
two.
By dropping the coins very carefully into the water edge-ways, it will
be found that even as many as five or six coins the size of a silver
dollar can be dropped into the water before it overflows.