CHAPTER V.

ON THE NATURE AND PROPERTIES OF LIGHT.

Section I.--_The compound Nature of Light._--Its decomposition into elementary coloured rays.--Division of these rays into Luminous, Heat-producing, and Chemical Rays 46

Section II.--_The Refraction of Light._--Phenomena of simple refraction by parallel and inclined surfaces.--Refraction from curved surfaces.--The various forms of Lenses.--The Foci of Lenses.--Formation of a Luminous Image by a Lens 49

Section III.--_The Photographic Camera._--Its simplest form.--The field of the Camera.--Chromatic aberration.--Spherical aberration.--The use of Stops.--The double, or Portrait combination of Lenses.--Variation between the Visual and Chemical Foci in Lenses 54

Section IV.--_The Photographic Action of Coloured Light._--Diagram of Chemical Spectrum.--Illustrative experiments.--Superior sensibility of Bromide of Silver to coloured light.--Mode in which dark-coloured objects are Photographed 60

Section V.--_On Binocular Vision and the Stereoscope._--Phenomena of Binocular Vision.--Theory of the Stereoscope.--Wheatstone's reflecting Stereoscope.--Brewster's Stereoscope.--Rules for taking Stereoscopic pictures 66