X CONTENTS. 



PAGE 



104. Nucleation due to gamma-rays 145 



105. Distribution of nucleation within the fog chamber. Radium 146 



106. The same continued. X-rays 146 



107. Origin of persistent X-ray nuclei 147 



108. Order of size of persistent X-ray nuclei 148 



109. Ordinary nuclei 149 



no. Ordinary dust-free air an aggregate of nuclei 149 



in. Nucleation of filtered air 150 



112. Nucleation of atmospheric air not filtered. Dust contents at Provi- 



dence 151 



113. The same continued. Dust contents of atmosphere at Providence 



and Block Island compared 152 



