Human mainly understand the surrounding condition by visual and audio informations, and do act to outer environments after processing these information~_ Undergraund operation environment is much different from those on surface Sound pl~opag. atl,)n in underground space may be affected by many acoustical factors which are ditferent w~y from surface It is important fc)r exact speech informatian transmission to know the sound propagation characteristic of underground space In this study, sound propagation experiments, articulation test of Japanese syllables, intelligibility test, transmission test and heariug judgment of Japanese vowels were conducted at an underground gallery with ventl]ation around 4 1 mlsec in a coal mine. From analy-Fxis of experimental data, it was found that sound propagatlon much depends on the relative directian between sound and ventilation, and sound attenuatian is rnoTe in the direction of tail wind, and recognition scores of speech Informations decreased quickly in proportion to distance from source And these results agreed with numerical calculatian using the sound ray equation app]ied to underground gallery with ventllation.

The　form　of　instabl】ity　in　Euler’s　probrem　of　elastic　column　buckling　have　been　known　as　divergence（or　statlc　instabll－ ity）．This　paper　attempts　to　investigate‘‘transitional　instability”in　dynamic　stability　of　nonhnear　elastic　column　under conservative　forces，The　term“transitional　instability”describes　instabUity　involving　transitional　motion　of　the　columns between　the　first　mode　and　the　higher　mode． The　equation　of　motion　and　the　boundary　conditions　in　the　probIem　of　the　isotropic，homogeneous，nonlinear　elastic bucklillg　are　sought．Numerical　solutions　for　this　nonlinear　boundary　value　problem　are　examined　by　caluculus　of　finite differellce．The　phenomenon　of　transitional　instability　seems　to　be　observed　in　the　long time　behavior　of　these　numerical solutions．