CONTENTS. Vll 

 CHAPTER VI. The Vibration of the Telephone Plate. 



PAGE 



49. Phenomena 55 



50. Interpretation. Lines. Oscillation about a vertical axis 56 



51. Shadow waves. Oscillation about horizontal axes 58 



52. Beating fringe-waves 58 



53. Effect of temperature. Miscellaneous observations 59 



54. Synchronism. Iron screw-core 61 



55. Shattered fringes 62 



56. Wave frequencies. Musical notes 63 



CHAPTER VII. Experiments Made in the Endeavor to Place the Revolving Mirror 



on the Interferometer. 



57. Apparatus. Revolving mirror normal 65 



58. Lens train 66 



59. Estimate 66 



60. The inclined revolving mirror and interferometer 67 



61. The revolving telescope objective 68 



62. Control fringes 69 



63. Sensitiveness 69 



64. Experiments with the rotating telescope. Fringes on washed images 70 



65. The combined revolving mirror and telescope 71 



CHAPTER VIII. On the Torsional Measurement of Variations of Acceleration 



of Gravity, by Interferences. 



66. Apparatus 74 



67. Measurements 76 



68. Thicker wire 77 



69. Equations 80 



70. Absolute viscosity of the wire 81 



71 . Twist in one direction only 82 



72. Observations on the permanently twisted wire 83 



73. Further experiments with the preceding apparatus 84 



CHAPTER IX. A Pneumatic Method of Measuring Variations of Acceleration 



of Gravity. 



74. Introductory 87 



75. Apparatus 87 



76. Equations 89 



77. Observations 90 



78. Sheathed or inclosed divers 93 



79. The swimmer under pressure 95 



80. Stems of small bore 97 



81. The diffusion of air through water in the lapse of years 98 



CHAPTER X. Gravitational Experiments, chiefly with Reference to the Accompanying 



Radiant Forces. 



82. Introductory 101 



83. Apparatus 101 



84. Long-period observations 102 



85. Long-period observations in the lapse of time 103 



86. Short-period observations 107 



87. Further observations no 



88. New apparatus 1 1 1 



89. Trial observations. Radiation effect 112 



90. Radiation effect observed on exhaustion 113 



91. Tendency of needle to stick to glass window 1 16 



92. Needle excursions under increasing pressure 1 16 



93. Experiments with the exhausted case 118 



94. Tentative estimate 1 19 



95. Angular velocity at different pressures 120 



96. Water-bath 120 



97. Attraction in vacuo 123 



98. Apparatus No. in. Brass and glass 124 



99. Metallic case cooled by efflux 128 



