AS A VEHICLE OE SOUND. 
215 
Were these results due to the fumes or to differences of temperature ? To the latter. 
The flame of a candle was placed at the tunnel end, and the hot air just above its tip 
was blown into the tunnel ; the action on the sensitive flame was decided. 
A red-hot iron was placed in the same position, and the heated air blown into the 
tunnel ; the action on the soundwvaves was decided. 
In both these cases the tunnel remained optically clear, while the same effect as that 
produced by resin, gunpowder, and phosphorus was observed. To differences of tempe- 
rature, therefore, and not to the fumes, the stoppage of the sound-waves in these cases 
was probably due. 
To arrive at certainty on this head, instead of the tunnel a cupboard with glass sides, 
constructed some years ago for experiments on the floating matter of the air, was 
employed. It was 3 feet long, 2 feet wide, and about 5 feet high. In the closed 
cupboard it was thought fumes might be generated and permitted to remain until 
differences of temperature had sensibly disappeared. Two apertures were made in two 
opposite panes of glass 3 feet asunder ; in front of one aperture was placed the bell, 
and behind the other, and at some distance from it, the sensitive flame. 
The flame being brought into that condition that a very slight action on the sound- 
waves sufficed to reduce it from agitation to quiescence, phosphorus placed in a cup 
floating on water was burnt within the closed cupboard. The fumes were very dense. 
Considerably less than the 3 feet traversed by the sound sufficed to extinguish totally 
a bright candle-flame. At first there was a slight action upon the sound ; but though 
the cloud remained of the same sensible density, the action rapidly vanished, and the 
flame was affected, as if the sound passed through pure air. 
The cupboard was next filled with the dense fumes of gunpowder. At first there was 
a slight action ; but this disappeared more rapidly than in the case of the phosphorus, 
the sound passing as if no fumes were there. It required less than half a minute to 
abolish the action in the case of the phosphorus, but a few seconds sufficed in the case 
of the gunpowder. The fumes were far more than sufficient to quench the candle- 
flame. 
The smoke of resin, very dense and white, was next introduced. With a density 
far more than sufficient to quench the candle, the action on the sound-pulse was 
sensibly nil. 
In this case the smoke was produced by bringing hot irons into contact with the resin. 
The same experiment was adopted with gum-mastic, the fumes of which produced no 
effect upon the sensitive flame. 
The fumes of the perchloride of tin, though of extraordinary density, exerted no 
sensible effect upon the sound. 
Exceedingly dense fumes of chloride of ammonium next filled the cupboard. A 
fraction of the length of the 3-foot tube sufficed to quench the candle-flame. Soon 
after the cupboard was filled the sound passed without the least sensible deterioration. 
An aperture at the top of the cupboard was opened ; but though a dense smoke-column 
