Pauehon has tested the hyt~othesls of many physicists, that the upper limit of audibility of any given~ear wtries with the intensity of the sound. Using a Cagniard-Latour siren, tie found that when the pressure of the steam, in the interior of lhe box, w~ries fYom 0"5 to 1"5 atmospheres, the limit of perceptibility corresponds to sounds which art comprised between 48,000 and 60,000 vii)rations per second. On increasing the steam pressure to 2"5 arm., giving the discs a rotation of 600 turns per second, he could hear the sound of 72,000 vibrations, which was the sharpest that he was able to prod,me. He then vibrated, longitudinally, metallie rods fixed at one extremity, hy rubhing them with rosined cloth. He tbund that the length of the rod which gives the limiting sound is, fbr any given metal, independent of the diameter. For steel, copper, and silver, the lengths are sensibly proportional to tile velocity of sound in those metals. By using an ear trumpet the limit of perceptibility is slightly increased, if the rods are excited with dilferent substances, such as rosin, turpeI~tlne, alcohol, ether, the limiting length changes and may vary t?om one to two. The sound which has ceased to be perceptible by the ear still acts powerfully upon a sensitive flame.--Coml~te.~ Rendus, April 9, 1883.
C.