CONTENTS. x iii 



SECTION XXL 



Polarization of Light Defined Polarization by Refraction Properties 

 of the Tourmaline Double Refraction All doubly Refracted Light is 

 Polarized Properties of Iceland Spar Tourmaline absorbs one of the 

 two Refracted Rays Undulations of Natural Light Undulations of 

 Polarized Light The Optic Axes of Crystals M. Fresnel's Disco- 

 veries on the Rays passing along the Optic Axis Polarization by 

 Reflection Page 179 



SECTION XXII. 



Phenomena exhibited by the Passage of Polarized Light through Mica and 

 Sulphate of Lime The Coloured Images produced by Polarized Light 

 passing through Crystals having one and two Optic Axes Circular 

 Polarization Elliptical Polarization Discoveries of MM. Biot, Fresnel, 

 and Professor Airy Coloured Images produced by the Interference of 

 Polarized Rays Fluorescence 186 



SECTION XXIII. 



Objections to the Undulatory Theory, from a difference in the Action of 

 Sound and Light under the same circumstances, removed The Disper- 

 sion of Light according to the Undulatory Theory Arago's final proof 

 that the Undulatory Theory is the Law of Nature 199 



SECTION XXIY. 



Chemical or Photographic Rays of Solar Spectrum Scheele, Ritter, and 

 Wollaston's Discoveries Wedgwood's and Sir Humphry Davy's Photo- 

 graphic Pictures The Calotype The Daguerreotype The Chroma- 

 type The Cyanotype Collodion Sir John Herschel's Discoveries in 

 the Chemical Spectrum M. Becquerel's Discoveries of Inactive Lines 

 in ditto Thermic Spectrum Phosphoric Spectrum Electrical Pro- 

 perties Parathermic Rays Moser and Hunt's Experiments Gene- 

 ral Structure and antagonist Properties of Solar Spectrum Defracted 

 Spectrum 203 



SECTION XXV. 



Size and Constitution of the Sun The Solar Spots Intensity of the 

 Sun's Light and Heat The Sun's Atmosphere His influence on the 

 Planets Atmospheres of the Planets The Moon has none Lunar 

 heat The Differential Telescope Temperature of Space Internal 

 Heat of the Earth Zone of constant Temperature Increase of Heat 

 with the Depth Central Heat Volcanic Action Quantity of Heat 

 received from the Sun Isogeothermal Lines Line of Perpetual Con- 

 gelation Climate Isothermal Lines Same quantity of Heat an- 

 nually received and radiated by the Earth 224 



