280 On the Froductmi of Sounds in Vapours. 



a green-house {une itiive), the temperature of which was 

 46° : then the sound became very sensible ; it was heard by 

 us, without incHning ourselves to the balloon, and even 

 through the door without the green-house; — there yet re- 

 mained in the balloon water in the liquid state : thus there 

 is no doubt of the producticm and propagation of sound in 

 watery vapour. 



When the balloon was taken out of the green -house its 

 temperature quickly fell : of course the principal part of 

 the vapour raised by the n)eans of temperature was pre- 

 cipitated ; the sound likewise appeared very sensibly dimi- 

 nished. Without making anv change in the apparatus, (he 

 same quantity of alcohol as water was introduced.' Water 

 considerefl as 1', the specific gravity of this alcohol was 

 0'823. The vapour fornied of this mixture was necessarily 

 of greater density and elasticity than that of water at the 

 same temperature; the sound too was much more sensible, 

 it was heard from the extremities of the rooms forming the 

 Museum of Natural History. Thus is sound also produced 

 and propagated in the vapour of alcohol. 



For our conclusive experiment we made tria'I of the va- 

 pour of ether : it was peculiarly interesting to us on account 

 of its great density and'elastic force, which are known to 

 be very considerable ; two circumstances which should in- 

 crease the intensity of the sound. The balloon was first 

 dried, as humidity diminishes the tension of the ether; 

 then the atmospheric air was freely allowed to enter until 

 an equilibrium was produced with the external pressure, 

 which was 0-7613 ; the balloon was taken into a long alley 

 in the garden, and the sound of the bell was found to be 

 sensible even to the distance of 145™ ; beyond this it be- 

 came so weak thai the sensation was not sufficiently distinct. 

 The temperature was 17" 75. Having measu'ed by this ex- 

 periment the inltnsity of sound produced in atmospheric 

 air, a vacuum was again made in the balloon, and more 

 sulphuric ether was introduced than the temperature could 

 raise in vapour. The specific gravity of this ether was 

 0-759; the elastic force of its vapour, measured by being- 

 introduced under a barometer purged pf air, was 0™ 35'49 

 at the tempeiature of 17-56. The bailoon being thus filled 

 with vapour was removed to the place where the preceding 

 experiment had been made, and the sound was ascertained 

 to be sensible at the distance of 131"''5, a convincing proof 

 that sound is produced and propagated in vapour as well as in 

 permanent gas. But we have proved that this can only be 

 effected by the instantaneous variatitms of temperature de- 

 8 ' tennincd 



