Mat 27, 1921] 



SCIENCE 



493 



ment; whereas if the pinhole is supplied on 

 the U side, this develops the usual pressure 

 increment. In the former case air leats 

 out of 0' diffusively; in the latter it leais 

 into 0". 



After many trials, however, only in one case 

 did I succeed in obtaining pressure decre- 

 ments with pinholes, screw cocks, etc.; this 

 when lost could not be recaptured; but all the 

 present and following results in acoustic 

 dilatation were strikingly reproduced by put- 

 ting a new telephone with unsealed plate in 

 circuit. 



With the apparatus. Fig. 1, and the cock C 

 opened at the critical point, a diapason c" 

 blown in the vicinity of the cock was easily 

 identified and the octave c'" even three times 

 as active (15 fringes). In another adjust- 

 ment, the shrill overtone gave nearly 100 

 fringes. There is some misgiving in inter- 

 preting these data, as the open mouth of the 

 pipe must usually be closed to the mouth of 

 the cock; but as the overtone was still appre- 

 ciably effective six inches to a foot away, the 

 results are probably trustworthy. 



8. Effect of Resonance. — While a parallel 

 relation of the maximum pressure to the 

 frequency of the telephone note has been 

 shown to exist, it is obvious that the best con- 

 ditions for high maxima will occur under 

 conditions of resonance between the natural B 

 and the T vibrations (Fig. 1) or their har- 

 monics. I, therefore, used the same small 

 induction coil with two storage cells, but with 

 a commutator-like current-breaker, controlled 

 by a small electric motor with a variable re- 

 sistance in circuit (electric siren). By grad- 

 ually decreasing this resistance all chromatic 

 intervals between about /' and a" were obtain- 

 able. The speed of the motor, however, fluc- 

 tuated slightly, while intervals within a semi- 

 tone often produced large pressure differences. 

 Thus the determinations of the intervals of 

 a somewhat flickering pitch in all chromatics 

 is quite difficult, even for a musical ear. A 

 series of organ pipes within the given range 

 seemed to offer the best standards of com- 

 parison, as it was necessary to turn rapidly 

 from one series of observations to another. 



In this way the graphs given, in Figs. 7, 8, 

 were worked out, the curves showing the 

 fringe displacement s to the logarithmic 

 frequency n of the telephone. In Fig. 7, to 

 limit the deflections within the range of the 

 ocular, about 2,000 ohms were put in circuit. 

 Three maxima and three minima (one posi- 

 tive and two negative) are indicated. The 

 maximum below /' could not be reached. The 

 strong one at c" was well marked and ap-, 

 proachable from both sides. The small one 

 near g", though easily observed by continu- 

 ously changing the pitch, was difficult to 

 record. 



The latter, however, is particularly inter- 

 esting as it introduces the strong pressure 

 decrements at a". I, therefore, reexamined it 

 in Fig. 8 with less resistance (1,000 ohms) in 

 circuit and the results came out more clearly. 

 The deep minimum at a" deserves further 

 investigation, as it precedes a probably very 

 high maximum at the near c'". At least this 

 may be inferred from the stimulation pro- 

 duced by an organ pipe used on the outside of, 

 the apparatus, §7. Something better than the 

 electrical siren used will have to be devised; 

 but apart from this the results are very 

 definite. 



Adjusting the siren for the maxinumi c", 

 the sensitiveness with different resistances in 

 circuit (2,000-9,000 ohms) was determined. 

 The curve is shown in series 9, Fig. 3, and is 

 the highest thus far obtained. The equation, 

 rs = constant, does not fit so well here, a 

 result inseparable from the slightly fluctu- 

 ating note; for this makes a big difference 

 in the maximum. The mean value is about 

 rs = 80 X 10^. Eef erred to a circuit resist- 

 ance of 100 ohms this is equivalent to a de- 

 flection of 800 fringes and a pressure of 

 Ap = .024 cm. of mercury. 



An auxiliary telephone placed in circuit 

 with that of T, Fig. 1, affords no suggestion 

 of these occurrences. Its notes rather increase 

 in strength regularly with the pitch. Yet if 

 the note should happen to be near e", the other 

 telephone would show no deflection. 



Finally the use of the pin hole vent as a 

 prohe to detect the distribution of compression 



