ILLUSTRATIONS. 



I'JG. PAGE 



1. Copy of Kepler's Diagram, explaining the Path of a Ray of Light 



through a Prism < 4 



2. Decomposition of Light by a Prism. Unequal Refrangibility of the 



Colours of the Spectrum "6 



3. Recomposition of "White Light by means of a Second Prism 8 



4. Experiment with a Candle 9 



5. Copy of Wollaston's Diagram 11 



6. Reduced Copy of Fraunhofer's Map 14 



7. Fraunhofer's Theodolite Spectroscope 15 



8. Showing Arrangement of Slit and Prism 24 



9. Introduction of a Lens to Produce an Image 25 



10. Direct-vision Prism with three Prisms, showing Path of Ray 27 



11. Direct- vision Prism with five Prisms , 27 



12. Improvised Bunsen Burner ... 28 



13. Method of Inserting Platinum Wire and Salt into Flame , . 29 



14. The Spectra of Continuous and Discontinuous Light Sources, the 



latter seen with a Line and Circular Slit 31 



15. The Spectrum of a Complicated Light Source as seen with a Circular 



and a Line Slit 32 



16. Copies of Herschel's Absorption Diagrams 36 



17. Diagram showing the increasing thickness of Air through which the 



Light of the Sun has to pass as it descends towards the horizon . 38 



18. Absorption of Sunlight by various thicknesses of a Solution of the Salts 



of Chromium (Gladstone) ... * 40 



19. Absorption of Sunlight by various thicknesses of a Solution of Potassic 



Permanganate (Gladstone) 40 



20. Method of Studying the Absorption of Iodine Vapour 41 



