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



of this character added to that of a gas-jet already on the point 

 of roaring is equivalent to an augmentation of pressure on the 

 issuing stream of gas." This explanation is, I believe, the only- 

 distinct one that has yet been given ; and I think the follow- 

 ing observations confirm and supplement it. I noticed that 

 if a sensitive flame be gently blown on through a glass tube, 

 while blowing on the flame it shrinks and diverges exactly as if 

 it were under the influence of sonorous vibration, and it diverges 

 the more strongly the nearer one blows to the root of the flame. 

 The flame also very forcibly diverges when a fiddle-bow is drawn 

 across or a wetted finger drawn down the metal or glass tube 

 which conveys the gas to the burner ; if the tube be of india- 

 rubber, giving it the slightest shake causes the flame to diverge, 

 a rapid fluttering of the flame being produced when the tube 

 oscillates. 



Professor Leconte has compared the movement of the flame to 

 that of a liquid vein under the influence of sonorous vibrations, 

 and has shown the striking resemblance between his observa- 

 tions on a gas-flame and Savart's experiments on jets of water. 

 The latter physicist has proved that certain notes cause a liquid 

 vein to emit a musical sound, and at the same time break up 

 into drops the portion of the jet which was previously conti- 

 nuous. The flame behaves in a precisely similar manner. I 

 have often noticed that, when rendered divergent by a sound, it 

 yields, more or less clearly, a musical note of slightly different 

 pitch. And I have lately ascertained, by examining the image 

 of the flame in a moving mirror (it is best to diminish the 

 brightness by smoking the glass), that, whilst the flame shown 

 in fig. 1 is continuous, the continuity is broken when the flame 

 is diverging under sonorous vibrations or flickering or roaring 

 under increased pressure. In this state fig. 2 becomes nothing 

 more than a succession of flames, resembling a singing flame or a 

 troubled liquid vein. 



To obtain perfect success in repeating these experiments, the 

 observations of Professor Leconte, Professor Tyndall, and the few 

 I have here detailed would show that regard must be had (a) 

 to the pressure of the gas, (b) the freedom of the gas-passages, 

 (c) the shape of the burner, (d) the size of the orifice. Atten- 

 tion to all of these cannot fail to give a flame sensitive to the 

 minutest noises : but, as I have endeavoured to show in the fore- 

 going note, success may be obtained by using gas direct from 

 the main, and merely attending to the shape of the burner — 

 choosing also the dusk of the evening as the best time for 

 making the experiments ; for then the pressure on the main ap- 

 pears to be at its maximum. 



