The receptacle at the top is filled with water, and the handle of the struck tuning fork is lowered into the water. The handle undergoes lengthwise simple harmonic motion, and its end transmits a compression wave through the water to the top of the box. The energy from the tuning fork thus sets up a standing wave in the resonator. If the tuning fork is withdrawn from the water, the sound coming from the resonator dies away slowly.

   The Mississippi apparatus is by Lerebours et Secretan of Paris, and the Colby apparatus by Rudolph Koenig of Paris.