ACOUSTICS AND GRAVITATION. 27 



In a majority of cases the action of the conical vent thus recalls the behavior 

 of the cup anemometer, as the pressure excess is on the concave side ; but the 

 lower curve of figure 35 (for R, smaller volume) is out of keeping with this, 

 as between lengths of 20 and 35 cm. of pipe the pressure excess is within, or 

 on the salient side. 



All attempts to use larger vents, together with wider external pipes (organ- 

 pipe form) , failed completely. It is supposed that with more powerfully reso- 

 nating external vessels, the pin-hole valve might be dispensed with, but no 

 corrcboration could be obtained. 



One may now argue that if in figure 33 a salient conical vent is attached to 

 the branch b', opening it to the atmosphere, and similarly a re-entrant vent to 

 the branch 6, the pressure difference within would be accentuated. Experi- 

 ments made both with the mercury interrupter and with the motor through 

 all available pitches distinctly negatived this surmise. The largest fringe 

 displacements were but one or two, determinable with certainty only by mul- 

 tiplication. Thus the pressure within the closed region is uniform in spite of 

 the reversed valves and the impulsive condensations of the telephone. 



26. Resonators of very large capacity. The volume of the region R', fig- 

 ure 14, was now further increased by adding an additional cylindrical tube, 

 6.2 cm. in diameter and 10.7 cm. high, closed on top with a glass plate. All 

 parts were (as before) carefully cemented together, thus completing resonator 

 III. The volume added was thus 370 cm. 3 , as compared with the original 

 48 cm. 3 , the ratio of volume increment being 6.7 and the ratio of total to 

 original volume 7.7. The conical vent c f , figure 14, here acted much better 

 than the copper-foil pin-holes, in the ratio of about 28 to 19 fringes at the 

 frequency n = 100 per second and resistance 100 ohms. At n = 12 per second 

 the conical vent gave about 15 fringes. 



Using the motor break and conical valve, the fringe displacements were 

 observed for frequencies between the notes g' and c'" and both with 1,000 

 ohms and 500 ohms in the telephone circuit. The results are comprehended 

 in the two curves in figure 36, the region R being in communication with 

 the atmosphere and R' closed, except as to the salient conical vent 

 specified. The curves are remarkable because of the sharpness of the 

 maxima, which are apparently overtones in the key of B or B\>. The 

 strong maximum near f" is fully obtained, also a small one near b', and indi- 

 cations of a large one again below g. The advantage of the salient conical 

 vent over one or more of the pin-holes in foil is shown in the small inset 

 at a (mercury interrupter, n= 100). It is obvious that the fundamentals of 

 the large closed reservoir R' will lie very low as compared with the 

 frequencies of the diagram, and very large fringe displacements may be 

 looked for there (27); but the present motor would not function below g\ 

 between a" and c'" the current seems to be uncertain. 



It was now thought desirable to test the conical vent in the re-entrant 

 position, and data of this kind are given by the curve, figure 37. All the 



