154 Lord Rayleigh's Acoustical Observations. 



The observations were made by moving the burner to and fro 

 in front of the board, until the positions were found in which the 

 flame was least disturbed by the sound; and it will be seen from 

 the results that these positions were very well defined. The 

 distances between the board and the orifice of the burner was 

 then taken with a pair of dividers, and measured on a scale 

 of millimetres. Two observers, J and E, adjusted the flame 

 independently of one another. The following are the results 

 obtained : — 



First position 



Second position 



Third position 



Fourth position ... 

 Fifth position 



J" J. 16$, 16$ mean 16$ 1 



\E. 16, 16 „ 16 J 



J J. 31, 3H „ 31^1 



16| 

 31| 



46| 



62i 



78i 



1625 

 15-7 

 15-6 



15-6 



15-5 



\E. 32^,31,32 „ 31|J 



[J. 47,47* „ 47^1 



IE. 46$, 47, 45$ ... ,,46*/ 



/J. 62,62$ „ 62H 



\E. 64, 60$, 62£ ... „ 62±J 



J. 78$, 78$..:. „ 78£ 



The second column contains the individual measurements 

 by the two observers ; the third shows the mean of all the 

 results for the same position. The numbers in the fourth 

 column are the results of dividing those of the third column 

 by 1, 2, 3, 4, 5, respectively, and agree very well together, 

 proving that the positions coincide with nodes. If the 

 positions had coincided with loops, the numbers of the third 

 column would have been in the ratios 1 : 3 : 5 : 7 : 9. The 

 wave-length of the sound was thus 31*2 mm., corresponding 

 to pitch /g. 



A few observations were made at the same time on the 

 positions of the silences, as estimated by the ear listening 

 through a tube. As was to be expected, they coincided with 

 the loops, bisecting the intervals given by the flame. When 

 the flame was in a position of minimum effect, and the free 

 end of the tube was held close to the burner at an equal 

 distance from the reflecting wall, the sound heard was a 

 maximum, and diminished when the end of the tube was 

 displaced a little in either direction. It may therefore be 

 taken as established that the flame is affected where the ear 

 would not be affected, and vice versa. 



Aerial Vibrations of very Loic Pitch maintained by Flames. 



In a lecture " On the Explanation of certain Acoustical 

 Phenomena," * I showed the production of a pure tone of 

 about 95 vibrations per second from a glass resonator and a 



* Proceedings of the Koyal Institution, March 15, 1875. Nature, vol. 

 xviii. p. 319. 



