It is a well-known fact that the intervention of an obstacle in the path of a beam of sound waves causes the formation of a shadow, but owing to the length of the waves the shadow is not so marked as for light. In 1826, Colladon made experiments which proved that sound shadows are more perfectly defined in water than in air. Prof John Le Conte has extended these observations, which he publishes in the Am. Jour. Science , 23, 27, Jan. 1882, under the tide "On Sound Shadows in Water."
The experiments were executed in 1874, during the engineering operations incident to the removal of "Rincon Rock," a sandstone reef in the harbor of San Francisco, by means of "surface blasting" with "giant powder" or dynamite. The depth of water on the reef was about fifteen feet at low tide, with an extreme tidal range of about six feet. The "cans" or "cartridges" of "giant powder" used contained each about fifteen pounds of the explosive compound, comprising about seventy-five per cent, of nitro-glycerine.