According to Chladini, the velocity of water is about four thousand nine hundred feet in a second, or between four and five times as great as it is in air." Different bodies conduct sound to the ear with more or less distinctness, according to their susceptibility for vibrating, and also with more or less rapidity. Ice, for example, conveys sound more speedily than water, and far more rapidly than air; thus, if a cannon on the edge of a frozen lake be fired, a person on the opposite side will find the flash to be followed by two reports, the first conducted to him by the ice, the second by the air. If a long steel rod be applied to the orifice of the ear, the gentlest jar given to its further extremity, and which, but for the intervention of the metal, would not have been audible, produces a strong and distinct impression. Cotton wool, sheeps' wool, and soft stuffs, generally are bad conductors of sound. The frozen earth conducts sound from great distances; the approach of a horseman in clear, frosty weather, will be heard at a far greater distance than when the ground is moist, or not hardened; in the former case, indeed, a double sound may sometimes be heard, one produced by the vibration of the ice-bound earth, the other, if distance allow, by that of the air. The distance to which sound can be conveyed through the speaking-trumpet is very surprising. The invention of the modern speaking-trumpet is generally accorded to sir Samuel Moreland, (1670,) and some of the large brass trumpets, made under his direction, carried the human voice from a mile and a half to between two and three miles distance. The efficiency of this instrument has been attributed to the repeated reflection of the sound, or waves of air, (like rays of light,) from side to side along the course of the tube, their ultimate efflux from the mouth of the instrument being in such a way, as either to cause the rays of sound to be collected into a focus at a distance, or to be projected forward in parallel lines, instead of allowing them to diverge in all directions, and on these principles various modifications in the form of the speaking-trumpet have been suggested.