[Illustration: FIG. 164.--Sprays of water show that the fork is in
motion.]
If a large dinner bell is rung, its motion or vibration may be felt on
touching it with the finger. If a tuning fork is made to give forth
sound by striking it against the knee, or hitting it with a rubber
hammer, and is then touched to the surface of water, small sprays of
water will be thrown out, showing that the prongs of the fork are in
rapid motion. (A rubber hammer is made by putting a piece of glass
tubing through a rubber cork.)
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