CONTENTS. IX 



NUCLEATION DUE TO GAMMA RAYS. 



PAGE 



67. Lead-cased wood fog chamber. Penetration 85 



68. The same continued 85 



69. The same continued. Effect of distance 87 



70. Glass fog chamber. Penetration 88 



71. The same continued. Radiation from a distance 89 



72. Distribution of nucleation along the axis, within the fog chamber 90 



73. General remarks 90 



CHAPTER IV. The Nucleation of the Atmosphere at Block Island, by 



Robinson Pierce, Jr. 



74. Introductory 91 



75. Apparatus 91 



76. Observations 101 



77. Remarks on the tables. Wood fog chamber 101 



78. Continued. Brass fog chamber 102 



79. Summary and comparisons 103 



80. Tentative inferences 107 



81. Average daily nucleations at Block Island 109 



82. Average monthly nucleations at Block Island no 



CHAPTER V. The Cotemporaneous Nucleations of the Atmosphere at 

 Providence and at Block Island. 



83. Introductory "i 



84. Observations in 



85. Comparison of the data for Providence and for Block Island 120 



86. Average daily nucleations 127 



87. Average monthly nucleations 128 



88. Conclusion 13 



CHAPTER VI. Summary and Conclusions. 



89. Introductory 132 



90. Notation 133 



91. Fleeting nuclei. Ions 133 



92. Fog limits of fleeting nuclei 134 



93. Persistent nuclei I 35 



94. Fleeting nuclei become persistent on solution. Origin of Rain 137 



95. Solutional enlargement of the nuclei of dust-free air 138 



96. Water nuclei. Solutional nuclei in general 14 



97. Alterations of large and small coronas. Periodic distributions of effi- 



cient nuclei in dust-free air i4 r 



98. Cause of periodicity 14* 



99. Persistence in general 14* 



100. Secondary generation 14* 



101. Space surrounding the X-ray tube a plenum of radiations 142 



102. Lead-cased fog chamber J 43 



103. Possibility of two kinds of radiation from the X-ray tube 145 



