xviii ILLUSTRATIONS. 



FIG. PAGE 



80. Arrangement for Photographically Determining the Coincidences of 



Solar Metallic Lines 212 



81. Another View of the Spectrum Photographic Arrangements . . . . 214 



82. Arrangement for obtaining Solar Spectrum alone 216 



83. Arrangement for obtaining Long and Short Lines 216 



84. Arrangement for obtaining and comparing Lines with Solar Spectrum 216 



85. Diagram showing process by which Impurities are Eliminated from Spectra 226 



86. Hypothetical Furnaces 237 



87. Hypothetic Furnaces. In this case the highest Temperature is not so 



high as in the former one 239 



88. The Varying Intensities of the Lines of Calcium as seen under different 



conditions 240 



89. The Varying Intensities of the Lines of Calcium with Increasing Tem- 



peratures 240 



90. The Various Intensities of the Lines of Magnesium as seen under 



different conditions 242 



91. The Various Intensities of the Lines of Magnesium arranged in order 



of Increasing Temperatures 242 



92. The Various Intensities of the Lines of Lithium under different con- 



ditions 243 



93. The Various Intensities of the Lines of Lithium arranged in order of 



Increasing Temperatures 243 



94. Stellar Spectra (Huggins) 247 



95. The Changes in the Spectrum of Calcium from the Bunsen Flame to 



Sirius 250 



96. Diagram showing how the Evolution of Chemical Forms may be indi- 



cated by their Spectra 261 



97. Diagram explaining that not all the Short Lines of Spectra need be 



true Products of High Temperature 291 



98. Hypothetical Spectra obtained on Distilling at successively Increasing 



Temperatures a Mixture of Light and Heavy Hydrocarbons ... 293 



99. Position of Spectroscope when Observing Vapours close to the Metal . 296 



100. Spectroscope and Lens when in Position for Observing Spectrum of 



Capillary 297 



101. Layers in Solar Atmosphere 304 



102. Lines produced by Layers are of Different Lengths 305 



103. But Lines of Different Length do not necessarily indicate that the sub- 



stances producing the longer of them extend down to the Photosphere 305 



