42 



DISPLACEMENT INTERFEROMETRY APPLIED TO 



obtainable from the c resonator (diameter 14 cm.), the dissipation in 3 

 dimensions being probably too severe. A repetition of this c" survey showed 

 that commutation had no appreciable effect ; but indications of a small flat 

 maximum near a' were now apparent. 



Similarly, a d" resonator suggested the small maximum at a', but the d" 

 was enormously developed, over twice as high and abrupt as the preceding 

 maximum for c". The same results were again obtained for an/ 7 ' resonator, 

 the maximum being very high and sharp. Beyond this the narrow aluminum 

 probe refused to function, the g" and a" resonators being characterized by 

 very small maxima at their respective pitches, less than one-third as high as in 

 the case for c" . 



The occurrence of the obscure maxima near a' induced me to replace the 

 narrow-tubed aluminum probe by a quill-tube glass probe, the same diameter 

 of pin-hole being used. The results so obtained with the c" resonator (given 

 in fig. 64) are quite different from the preceding graph for c", inasmuch as the 

 a' maximum is now highly developed. The apparatus, moreover, is so much 

 more sensitive (auxiliary resistance here removed) that even 1,000 ohms may 

 be put in the telephone circuit with the distinct data seen in the lower curve. 

 The effect of commutation is again absent, the numbers I and 77 in the 

 curve referring to the position of the switch. 



66 



d 



<J 



a' c' d' e" * a" a' c" d" a' c? 



Very different from this is the behavior of the d" resonator, figure 65. The 

 graphs for the two positions (7 and 77) of the telephone switch differ radically. 

 In both the a' maximum is present, but strong only in the position 77. On the 

 other hand, the important d" maximum strong in position 7 quite loses its 

 prominence in position 77. Results for the /", g" , a" resonators were in a 

 similar manner complicated. All carried the a' maximum, but the strength 

 of the primary maxima f", g", a", still prominent in f", soon fell off and could 

 scarcely be detected in the a" resonator, in spite of the quill-tube probe and 

 the absence of extra resistance in circuit. 



The presence of the a' maximum in all the graphs, apart from their pitch, 

 proves conclusively that this note arises in the reservoir of the U-tube. For 



