Theories of the Nature of Light--Hypotheses of Newton and Huygens--Sources of Light--The Sun--Velocity of Light--Transparency--Dark Lines of the Spectrum--Absorption of Light--Colour--Prismatic Analysis--Rays of the Spectrum--Rainbow--Diffraction--Interference--Goethe’s Theory--Polarisation--Magnetisation of Light--Vision--The Eye--Analogy--Sound and Light--Influence of Light on Animals and Vegetables--Phosphorescence arising from several Causes--Artificial Light--Its Colour dependent on Matter 118
The Sun-ray and its Powers--Darkening of Horn Silver--Niepce’s Discovery--Prismatic Spectrum--Refrangibility of Light, Heat, and Actinism--Daguerre’s Discovery--Photography--Chemical Effects produced by Solar Radiations--Absorption of Actinism--Phenomena of the Daguerreotype--Chemical Change produced upon all Bodies--Power of Matter to restore its Condition--Light protects from Chemical Change--Photographs taken in Darkness--Chemical Effects of Light on organized Forms--Chemical Effects of Solar Heat--Influence of Actinism on Electricity--Radiations in Darkness--Moser’s Discoveries, &c. 166
Discovery of Electrical Force--Diffused through all Matter--What is Electricity?--Theories--Frictional Electricity--Conducting Power of Bodies--Hypothesis of two Fluids--Electrical Images--Galvanic Electricity--Effects on Animals--Chemistry of Galvanic Battery--Electricity of a Drop of Water--Electro-chemical Action--Electrical Currents--Thermo-Electricity--Animal Electricity--Gymnotus--Torpedo--Atmospheric Electricity--Lightning Conductors--Earth’s Magnetism due to Electrical Currents--Influence on Vitality--Animal and Vegetable Development--Terrestrial Currents--Electricity of Mineral Veins--Electrotype--Influence of Heat, Light, and Actinism on Electrical Phenomena 193
Magnetic Iron--Knowledge of, by the Ancients--Artificial Magnets--Electro-Magnets--Electro-Magnetism--Magneto- Electricity--Theories of Magnetism--The Magnetic Power of soft Iron and Steel--Influence of Heat on Magnetism--Terrestrial Magnetism--Declination of the Compass-needle--Variation of the Earth’s Magnetism--Magnetic Poles--Hansteen’s Speculations--Monthly and Diurnal Variation--Dip and Intensity--Thermo-Magnetism--Aurora Borealis--Magnetic Storms--Magnetic conditions of Matter--Diamagnetism, &c. 235