Introductory — Uses of Experiment — Early Scientific Notions — Sciences of Observation — Knowledge of the Ancients regarding Light — Defects of the Eye — Our Instruments — Rectilineal Propagation of Light — Law of Incidence and Reflection — Sterility of the Middle Ages — Refraction — Discovery of Snell — Partial and Total Reflection — Velocity of Light — Roemer, Bradley, Foucault, and Fizeau — Principle of Least Action — Descartes and the Rainbow — Newton’s Experiments on the Composition of Solar Light — His Mistake regarding Achromatism — Synthesis of White Light — Yellow and Blue Lights produce White by their Mixture — Colours of Natural Bodies — Absorption — Mixture of Pigments contrasted with Mixture of Lights
Origin of Physical Theories — Scope of the Imagination — Newton and the Emission Theory — Verification of Physical Theories — The Luminiferous Ether — Wave-theory of Light — Thomas Young — Fresnel and Arago — Conception of Wave-motion — Interference of Waves — Constitution of Sound-waves — Analogies of Sound and Light — Illustrations of Wave-motion — Interference of Sound Waves — Optical Illustrations — Pitch and Colour — Lengths of the Waves of Light and Rates of Vibration of the — Ether-particles — Interference of Light — Phenomena which first suggested the Undulatory Theory — Boyle and Hooke — The Colours of thin Plates — The Soap-bubble — Newton’s Rings — Theory of ‘Fits’ — Its Explanation of the Rings — Overthrow of the Theory — Diffraction of Light — Colours produced by Diffraction — Colours of Mother-of-Pearl.
Relation of Theories to Experience — Origin of the Notion of the Attraction of Gravitation — Notion of Polarity, how generated — Atomic Polarity — Structural Arrangements due to Polarity — Architecture of Crystals considered as an Introduction to their — Action upon Light — Notion of Atomic Polarity applied to Crystalline Structure — Experimental Illustrations — Crystallization of Water — Expansion by Heat and by Cold — Deportment of Water considered and explained — Bearings of Crystallization on Optical Phenomena — Refraction — Double Refraction — Polarization — Action of Tourmaline — Character of the Beams emergent from Iceland Spar — Polarization by ordinary Refraction and Reflection — Depolarization.
Chromatic Phenomena produced by Crystals in Polarized Light — The Nicol Prism — Polarizer and Analyzer — Action of Thick and Thin Plates of Selenite — Colours dependent on Thickness — Resolution of Polarized Beam into two others by the Selenite — One of them more retarded than the other — Recompounding of the two Systems of Waves by the Analyzer — Interference thus rendered possible — Consequent Production of Colours — Action of Bodies mechanically strained or pressed — Action of Sonorous Vibrations — Action of Glass strained or pressed by Heat — Circular Polarization — Chromatic Phenomena produced by Quartz — The Magnetization of Light — Rings surrounding the Axes of Crystals — Biaxal and Uniaxal Crystals — Grasp of the Undulatory Theory — The Colour and Polarization of Sky-light — Generation of Artificial Skies.
Range of Vision not commensurate with Range of Radiation — The Ultra-violet Rays — Fluorescence — The rendering of invisible Rays visible — Vision not the only Sense appealed to by the Solar and Electric Beam — Heat of Beam — Combustion by Total Beam at the Foci of Mirrors and Lenses — Combustion through Ice-lens — Ignition of Diamond — Search for the Rays here effective — Sir William Herschel’s Discovery of dark Solar Rays — Invisible Rays the Basis of the Visible — Detachment by a Ray-filter of the Invisible Rays from the Visible — Combustion at Dark Foci — Conversion of Heat-rays into Light-rays — Calorescence — Part played in Nature by Dark Rays — Identity of Light and Radiant Heat — Invisible Images — Reflection, Refraction, Plane Polarization, Depolarization, Circular Polarization, Double Refraction, and Magnetization of Radiant Heat
Principles of Spectrum Analysis — Prismatic Analysis of the Light of Incandescent Vapours — Discontinuous Spectra — Spectrum Bands proved by Bunsen and Kirchhoff to be characteristic of the Vapour — Discovery of Rubidium, Cæsium, and Thallium — Relation of Emission to Absorption — The Lines of Fraunhofer — Their Explanation by Kirchhoff — Solar Chemistry involved in this Explanation — Foucault’s Experiment — Principles of Absorption — Analogy of Sound and Light — Experimental Demonstration of this Analogy — Recent Applications of the Spectroscope — Summary and Conclusion
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