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THE POPULAR SCIENCE MONTHLY. 



The vapor of water at ordinary temperatures is so small in quan- 

 tity, and so attenuated, that it requires special precautions to bring 

 out its action. But with such precautions it was found competent to 

 reduce to quiescence the sensitive flame. 



As the skill and knowledge of the experimenter augment, he is often 

 able to simplify his experimental combinations. Thus, in the present 

 instance, by the suitable arrangement of the source of sound and the 

 sensitive flame, it was found that not only twenty-five layers, but three 

 or four layers of coal-gas and carbonic acid, sufficed to still the agitated 

 flame. Nay, with improved manipulation the action of a single layer 

 of either gas was rendered perfectly sensible. So also as regards 

 heated layers of air, not only were sixty-six or twenty-two heated plati- 

 num wires found, sufficient, but the heated air from two or three candle- 

 flames, or even from a single flame, or a heated poker, was found per- 

 fectly competent to stop the flame's agitation. The same remark ap- 

 plies to vapors. Three or four layers of air saturated with the vapor 

 of a volatile liquid stilled the flame ; and, by improved manipulation, 

 the action of a single saturated layer could be rendered sensible. In 

 all these cases, moreover, a small, high-pitched reed might be substi- 

 tuted for the bell. 



I 



Fig. 2. Apparatus for illustrating the Reflection of Sound in a Non-homogeneous 



Atmosphere. 



In the experiments at the South Foreland, not only was it proved 

 that the acoustic clouds stopped the sound, but in the proper position 

 the sounds which had been refused transmission were received by re- 

 flection. I wished very much to render this echoed sound evident ex- 

 perimentally, and stated to my assistant that we ought to be able to 

 accomplish this. Mr. Cottrell met my desire by the following beautiful 

 experiment, which has been thus described before the Koyal Society: 



" A vibrating reed B (Fig. 2) was placed so as to send sound-waves 



