Mr. W. F. Barrett on Sensitive Flames. 289 



do not establish, the theoretical explanation I have offered, yet 

 I sought directly to determine its truth by examining the state 

 of the current of gas in the pipe. For this purpose a burner 

 was attached to a long length of glass tubing and the stream, of 

 gas rendered visible by passing it through two bulbed tubes, 

 the first containing hydrochloric acid, the second ammonia. 

 The dense fumes of amnionic chloride thus formed tracked the 

 passage of the gas through its conduit, and clearly marked the 

 unignited column of gas rising from the burner. Owing per- 

 haps to the narrow diameter of my tube I could not detect any 

 change in the appearance of the smoke passing through it whilst 

 a sound was being made. A new and most instructive effect 

 was, however, observed. The column of unignited gas was as 

 sensitive to the influence of sound as the flame itself, shrinking 

 and diverging at a whistle, a clap of the hands,, &c, just as did 

 the flame. 



Substituting air for the coal-gas, I forced a stream of the 

 former through the same apparatus, employing as the nipple 

 from which the air issued a steatite burner having a circular ori- 

 fice "046 inch in diameter, a burner which with coal-gas under 

 an increased pressure (about 3J inches of water) gives a most 

 sensitive flame. Gently urging the air from the bag, a slender 

 stream of smoke was obtained which, when undisturbed, rose to a 

 height of 14 inches before it broke and scattered into a divergent 

 head. The sound of a whistle instantly brought this head down 

 to a height of only an inch above the nipple : so swift and large 

 a fall astonished me greatly; for it exceeded anything I had ob- 

 tained with flames. So wonderfully sensitive was this column 

 of smoky air that, although the pressure was kept constant, 

 yet it was rarely still for long together, the recurrence of little 

 noises, and inaudible vibrations communicated to the room, con- 

 stantly disturbed and shivered the fragile thing. In fact, to 

 certain notes this stream of air was far more sensitive than 

 the most sensitive flame I have ever obtained. This greater 

 sensitiveness of the air might be expected, as it is unattended with 

 the upward draught of the long column of heated air which ac- 

 companies the flame. But not to the same notes were the air 

 and the flame equally sensitive ; for comparatively low notes influ- 

 enced the stream of air, whilst the sound of a hiss, so energetic in 

 its action on the flame given by this burner, had but little effect on 

 the column of smoky air. This is accounted for by the fact that 

 the velocity of the stream of air was much less than that of 

 the stream of gas ; and, as a general rule, the less the velocity 

 of the stream of gas the graver the note which affects the flame. 



When a sound, as of a whistle, was sustained and loud, it 

 could be seen that the brush-like head of the column was broken 



Phil. Mag. S. 4. Vol. 33. No. 2.23. April 1867. U 



