Fig. 14.—Joined by air.
As the atmospheric pressure is much greater than the pressure from within, the plate remains firmly fixed to the glass ([Fig. 14]).
Glass Raising Extraordinary
This experiment, similar in principle to the last, is quite as striking in its effect.
It consists of raising in air a glass filled with water, by causing it to adhere to the hand when the latter is held quite open.
With the last experiment fresh in our minds, it is not difficult to guess that this phenomenon is due to the existence of a partial vacuum under the hand, but it is not so easy to know how to obtain this vacuum.
The means of carrying out the experiments are as follows:—
Put the glass filled with water on the table, and over the top place the palm of the hand, taking care that the four fingers are bent almost at right angles, as shown in the first of the accompanying figures ([Fig. 15]).
If, continuing to press the palm of the hand on the edge of the glass, you raise the four fingers quickly, thus having the palm stretched out, you will force out most of the air which is between your palm and the surface of the water, and in this way you will produce under your hand a partial vacuum. This vacuum will be sufficient to allow the atmospheric pressure to overcome the weight of the glass and its contents; thus a sucker is formed which allows the glass to remain attached to the hand ([Fig. 16]).