lass 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, Caesium, 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

APPENDIX.

On the Spectra of Polarized Light

Measurement of the Waves of Light

INDEX

ON LIGHT

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 LI