[. 28aa4 
XXIX. On a Method of Mechanically Reinforcing Sounds. 
‘By T. Cy Porter; 27. A.* , 
[Plate XVI. ] 
T is now about ten years since a friend, Mr. A. J. Jex- 
Blake, first drew my attention to the fact that if a small 
tuning-fork be struck and then held in the flame of a bunsen- 
burner the loudness of its note is very materially increased ; 
at that time the explanation, though simple, did not occur to 
me, and although I mentioned the fact to two or three 
physicists, they did not suggest the cause. 
That the phenomenon is not a case of ordinary resonance 
is proved by the fact that no increase in the loudness of the 
note is observed if the fork is held over the burner, either 
with or without the gas turned on; nor when the length of 
the tube of the burner is altered so that it would naturally 
respond, when filled with the mixture of gas and air, to the 
pitch of the fork employed. There is, in this case, some 
resonance, but it is very much fainter than the reinforcement 
we are considering. 
Further, if the fork be held in the luminous flame from 
the same burner, caused by stopping up its holes, the sound 
is slightly louder, so that it is the action of the rarefactions 
and condensations of the sound-waves in the burnzng mixture 
of gas and air which gives rise to the increased loudness. 
The following experiment shows this admirably. A piece of 
wire gauze is supported about three-quarters of an inch 
above the bunsen, and the issuing mixture of gases ignited 
above the gauze, and the supply of gas and air so adjusted 
that the flame is all blue, and nearly quiet ; if the fork be 
then held in the flame there is a very marked increase of 
loudness, whilst if it be held, as it easily can with a little 
care, between the gauze and the top of the burner, there is 
scarcely any augmentation of the sound. 
If the various parts of a bunsen flame be explored with a 
sounding fork it will be found that there is the greatest 
effect in the hottest part of the flame, z. e. in that part where 
the most rapid chemical action is proceeding, and if ex- 
periments are made to compare the effects of the luminous 
and nonluminous flames of the same bunsen-burner, it appears 
that the latter is the more energetic, though the reinforce- 
ment caused by the former is very considerable. The effect 
of the sound-pulses is probably therefore to change the con- 
tinuous flame of the burner into one which is more or less 
* Communicated by the Physical Society: read December 11, 190. 
