CONTENTS. 



CHAPTER I. The Open Mercury Manometer read by Displacement 



Inter ferometry. 



PAGE 



1. Apparatus I 



2. Experiments I 



3. Equations and pressure observations 2 



4. Air thermometer 3 



5. Acoustic pressure, etc 4 



CHAPTER II. The Interferometer U-tube used as an Absolute Electrometer. 



6. Electrical condenser 5 



7. Fringes from a free mercury surface 6 



8. Equations 6 



9. Specific inductive capacity 9 



10. Allowance for the electrometer 10 



11. Absolute values 1 1 



12. Improvements and miscellaneous experiments 12 



CHAPTER III. Acoustic Pressures and Dilatations chiefly in Reservoirs. 



13. Introductory. Apparatus 14 



14. Observations. Closed and open resonators 15 



15. Resonator all but closed 15 



1 6. Pressure depending on the frequency and on the intensity of vibration 1 6 



17. Fringe deflection varies as current intensity 16 



18. Pin-hole sound-leaks 17 



19. Effect of resonance 18 



20. Inside and outside stimulation 20 



21. Apparent removal of pressure decrements 21 



22. Reversal of poles of telephones changes sign of fringe deflection 23 



23. Change of volume of reservoir 24 



24. U-tube used differentially 24 



25. Conical vents reversible. Periodicity 26 



26. Resonators of very large capacity 27 



27. Resonators of very small capacity 28 



CHAPTER IV. The Pin-hole Probe for Sound Pressures. 



28. The pin-hole sonde, or probe 3 1 



29. Pressures in smooth, straight pipes 33 



30. Symmetrical induction 35 



31. Closed region with pipe 36 



32. Closed organ-pipe 37 



33. Open pipes and adjutages 37 



34. Reversal of poles of telephone 38 



35. Open pipe on the interferometer 4 



36. Helmholtz spherical resonator 4 1 



37. Correlative experiments with the torsion balance 43 



38. Conclusion 44 



CHAPTER V. The Compression of a Sound Wave in Diapason Pipes. 



39. Introduction 46 



40. Apparatus 46 



41. Observations with crossed pipes 47 



42. Deductions 47 



43. Stroboscopic and other secondary phenomena 48 



44. Observations with longitudinal pipes 49 



45. Organ-pipe blower 50 



46. Interference 51 



47. Reed pipes, voice 52 



48. General result 53 



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