Six Lectures on Light, by John Tyndall

Table of Contents

Preface to the Fourth Edition.

Lecture i.

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

Lecture ii.

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.

Lecture iii.

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.

Lecture iv.

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.

Lecture v.

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

Lecture vi.

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


  1. On the Spectra of Polarized Light.
  2. Measurement of the Waves of Light.
Sir Thomas Laurence PRA Pinx Henry Adlarc. Sc.
(Signature) Thomas Young

Last updated Tuesday, March 4, 2014 at 20:21