Solar and Terrestrial Heat--Position of the Earth in the Solar System--Heat and Light associated in the Sunbeam--Transparency of Bodies to Heat--Heating Powers of the Coloured Rays of the Spectrum--Undulatory Theory--Conducting Property of the Earth’s Crust--Convection--Radiation--Action of the Atmosphere on Heat Rays--Peculiar Heat Rays--Absorption and Radiation of Heat by dissimilar Bodies--Changes in the Constitution of Solar Beam--Differences between Transmitted and Reflected Solar Heat--Phenomena of Dew--Action of Solar Heat of the Ocean--Circulation of Heat by the Atmosphere and the Ocean--Heat of the Earth--Mean Temperature--Central Heat--Constant Radiation of Heat Rays from all Bodies--Thermography--Action of Heat on Molecular Arrangements--Sources of Terrestrial Heat--Latent Heat of Bodies--Animal Heat--Eremacausis--Spheroidal State Cold--Condensation--Freezing--Theories of Heat--Natural Phenomena--and Philosophical Conclusion 62 CHAPTER VII. LIGHT. 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 CHAPTER VIII. ACTINISM--CHEMICAL RADIATIONS. 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 CHAPTER IX. ELECTRICITY.