Mr. F. W. Barrett on Sensitive Flames. 219 



obtained with the longest and most voluminous flames. Having 

 found the best size for the burner, I now altered its shape by 

 carefully snipping and filing the orifice. It was at once noticed 

 that the shape as well as the size of the burner was an important 

 element in the production of the phenomenon. Metal burners 

 with circular orifices, after adjusting by repeated trials their size 

 and shape, answered equally as well as glass ones. The stem of 

 a tobacco-pipe does not answer for a burner ; the bore is too 

 small ; but a gas-fitter's brass blowpipe, if straightened and filed 

 to a rather larger aperture, makes a very fair burner. On ac- 

 count, however, of the ease with which they can be reproduced, 

 I preferred in general to use burners formed of glass tubing. 

 By care a burner was obtained which gave a remarkably sensi- 

 tive flame ; this burner is represented in fig. 3. It is formed of 

 glass tubing about | of an inch in diameter, contracted to an 

 orifice ^ of an inch in diameter. It is very essential that this 

 orifice should be slightly V-shaped, as shown in the figure*. 



When this burner was connected by a length of india-rubber 

 tubing to the gas-pipes, the stopcock being fully open, a tapering 

 flame about 15 inches long was obtained (fig. 1). With this 

 flame the following experiments were made. 



A noise of any kind — walking on the ground, shutting a book, 

 or stamping a chair, for example — caused the flame to shrink 

 down more or less. Its action was like that of a sensitive, ner- 

 vous person uneasily starting and twitching at every little noise. 

 These noises consisting of a mixture of notes, the experiment 

 was purified by trying a series of tuning-forks of different pitch, 

 ranging from 256 to 512 vibrations per second. It was found 

 that none of the fundamental notes of these forks caused the flame 

 to shrink ; but a fork of higher pitch, or the higher notes of the 

 series of large forks, instantly caused a divergence of the flame f. 

 A large inverted bell was sounded by a violin-bow and caused to 

 yield one of its higher harmonics. The flame was intensely influ- 

 enced ; and a very pretty effect was here observed : the beats (due 

 to the interference of the vibrations of the bell), which were faintly 

 audible, were rendered more apparent by the movements of the 

 flame ; at every beat the momentary silence allowed the flame 

 partially to regain its original height, from which, however, it 

 was almost immediately thrown down by the sound which fol- 



* Nothing is easier than to form such a burner ; it is only necessary to 

 draw out a piece of glass tubing in a gas-flame, and with a pair of scissors 

 snip the contraction into the shape indicated. 



t This and the next experiment I made at the Royal Institution in 

 June 1866. The influence of pitch on the flame is well illustrated by 

 running up the scale of a pianoforte : when the high notes are approached 

 the flame becomes uneasy, and at last diverges strongly when the note 

 equals about 1500 vibrations per second. 



