288 Mr. W. P. Barrett on Sensitive Flames. 



flame ought therefore to be in a state of vibration : this is the 

 case. Moreover the gas will ripple through the burner with a 

 rhythmic flow timed to the pitch of the exciting sound ; and 

 therefore the rate of this vibration of the flame should vary with 

 the pitch of the note : I have found this also to be the case. The 

 louder and more sustained the exciting sound, the greater the 

 amplitude and the more continuous the vibrations of the gas- 

 pipe ; and hence the greater should be the effect on the current 

 of gas and thus on the flame : this is so. The higher the pitch 

 of the sound, the more rapid the vibrations of the pipe and the 

 greater the disturbance of the gas within ; hence there should be 

 a more marked effect with such notes : and this is well known 

 to be the case. A sound excited contiguous to the pipe, even if 

 far distant from the flame, should have more effect than away 

 from the pipe at the same distance : this is so. A contraction 

 of the gas-pipe near the burner should cause a greater velo- 

 city of the gas, and ought, therefore, to produce a somewhat 

 similar action to a sound : it does so, as is easily proved by 

 pinching a flexible tube near the burner; the flame at once 

 shrinks and roars; and if a Bunsen's screw-clip be used to pinch 

 the tubing, it will be seen how wonderfully small a pressure on 

 the screw is sufficient to cause the shrinking and roaring of the 

 flame when near its sensitive point. Hence, mechanically 

 checking the flow of gas near the point where it issues from the 

 burner should disguise the effect produced by the sonorous vi- 

 brations, and the more effectually if the gas pass through an 

 oblique as well as a contracted channel : this is the case, a par- 

 tially turned stopcock at all near the burner being fatal to a 

 sensitive flame. Many feet of free tubing should thus be neces- 

 sary, after the stopcock, in order to abolish the ricochetting of 

 the current of the gas from side to side of the pipe, and allow 

 the stream to resume its tranquil flow* : and this is found to be 

 the case, Professor Tyndall having remarked, as an essential 

 condition of success, " that a free way should be open for the 

 transmission of the vibrations from the flame, backwards, through 

 the gas-pipe which feeds it," — not, however, for this reason, I 

 believe, but that a current of gas filling the tube and of equal 

 density throughout is necessary, in order that the feeble vibra- 

 tions of the pipe may be impressed on and retained by the stream 

 of gas. The material and thickness, as well as the length of 

 the gas-pipe, should cause a difference in the result; and I believe 

 such a difference can be detected with various kinds of tubing. 

 Although the foregoing observations strongly support, if they 



* I am indebted to Mr. Sugg, the eminent gas engineer, for information 

 on this among other points, he having ascertained that such a ricochet- 

 ting of a current of gas can be produced. 



