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. 103
POULTRY FOUNTAIN