W. L. Stevens — Sensitive Flame as a means of Research. 257 



Akt. XXYIII. — The Sensitive Flame a>s a means of Research ; 

 by W. LeConte Stevens. 



A little over thirty years ago the discovery was published 

 in this Journal* that under certain conditions a naked flame of 

 illuminating gas may become sensitive to sonorous vibrations. 

 Nine years elapsed before any development grew out of this 

 acquisition to science. In 1867, Mr. W. F. Barrett, who was at 

 that time an assistant in the laboratory of the Royal Institution, 

 published his independent discovery of the sensitiveness of 

 flame; and the use of the manometric flame, in the hands of 

 Rudolph Koenig, was subsequently developed with great skill 

 for the analysis of compound tones. The use of Professor 

 Barrett's flame has become widely known, especially through 

 the familiar volume of lectures on Sound by Professor Tyndall. 

 Govi in Italy, Barry in England, and Geyer in America inde- 

 pendently discovered the method of securing a sensitive flame, 

 with no pressure higher than that of the ordinary street mains, 

 by causing air to mingle with the gas after it issues from the 

 nozzle, and allowing the mixture to burn after passing through 

 wire gauze While this flame may be made exquisitely sensi- 

 tive, it is not so convenient in practice as the high pressure 

 flame of Professor Barrett. It is well known that these flames 

 are usually sensitive only to sounds of high pitch, and through 

 a limited range of pitch, this range becoming generally narrower 

 with increase of sensitiveness. During the last few years Lord 

 Rayleigh has used the sensitive flame with signal success in 

 studying certain analogies between sound and light. His inter- 

 esting lecture on " Diffraction of Sound," delivered a little over 

 a, year ago before the Royal Institution, f served as my starting 

 point ; and I am further indebted to him for special instruc- 

 tions without which I should perhaps not have succeeded in 

 performing satisfactorily all the experiments mentioned in his 

 lecture. As this lecture has not thus far been re-published in 

 America, a brief resume of it may possibly be acceptable. 



Waves of light are so short that special precautions are 

 needed to exhibit the phenomena of diffraction. Light ema- 

 nating from a point and interrupted by an obstacle produces a 

 shadow that may be regarded for all practical purposes as geo- 

 metric. Waves of audible sound, on the contrary, are so long 

 that when an obstacle is interposed the effect of diffraction 

 masks that of radial propagation, and hence it is not usually 



* On the influence of Musical Sounds upon the Flame of a jet of Coal-gas. By- 

 John LeConte. This Journal, January, 1858. 



\ Proceedings of the Royal Institution of Great Britain, Jan. 20, 1883. 



