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



table, and allowing the waves reflected from it to interfere with 

 those radiated directly from the whistle. The effect is obviously 

 the same as if they proceeded from two sources, but interfer- 

 ence bands can be produced on only one side of the median 

 line. In the accompanying diagram AM is the plane of the 

 mirror, S the source of sound, and S' the virtual source from 

 which the reflected waves may be regarded as coming. Let 

 the nozzle from which the flame issues be placed first at A and 

 then lifted vertically. The flame will flare at the points B, C, 

 D, etc., whose distances respectively from S and S 7 differ by 

 an even number of half wave-lengths. Midway between A 



and B, B and C, etc., are points of complete interference where 

 the frame should burn quietly. The distance AB is approxi- 



AjVT 

 mately equal to -^i. The accompanying table gives a com- 

 parison between the results of theory and experiment, in which 

 the height of the whistle above the table, MS, is 10 inches ; 

 the distance AM is 36 inches, and the wave length, X, is l - 05 

 inch. The successive measurements are of distances above the 

 table at which the flame became quiescent. The first column 

 is calculated from the formula ; the others are the records from 

 five sets of experiments. 



Theory. 



I 



II 



III 



IV 



V 



•945 



•9 



1-0 



•9 



1-0 



1-0 



2-835 



2-8 



2.7 



2-7 



2-8 



2-9 



4-725 



4-7 



4-6 



4-7 



4-9 



4-7 



6615 



6-7 



6-7 



6 7 



69 



6-7 



8-505 



8.9 



9-0 



8-8 



90 



9-1 



10-395 



11-0 



11-3 



11.0 



11-2 



11-3 



12-285 





13 6 







13-6 



13-6 



The sensitive flame is not applicable for purposes of exact 

 measurement, as these experiments show ; but it is much more 

 nearly so than has been generally supposed. Without its aid 

 there would have been no possibility of establishing these im- 

 portant analogies between light and sound. 



