Fill a tumbler with water, press your palm down on the top with your fingers pointing downward (Fig. 101), straighten your fingers without admitting air to the turn-tier, and then lift your hand. Do you lift the tumbler of water also?

There is a partial vacuum between your hand and the water, and the atmospheric pressure upward and downward holds your hand and the tumbler together.

Experiment 78. A Magic Pendulum

Pass a string through a small hole in a piece of cardboard, knot the end of the string, and drop melted candle wax over the hole to make it air tight.

Fill a tumbler with water, press the cardboard down on the tumbler with the palm of your hand, and lift the string. Do you also lift the tumbler (Fig. 102) ?

Swing the tumbler gently as a pendulum.

Fig. 102. Tumbler Pendulum