Six Lectures On Light

Chromatic Phenomena produced by Crystals in Polarized Light -- The Nicol Prism -- Polarizer and Analyzer -- Action of Thick and Thin Plates of Selenite -- Colors dependent on Thickness -- Resolution of Polarized Beam into two others by the Selenite -- One of them more retarded than the other -- Recompounding of the two Systems of Waves by the Analyzer -- Interference thus rendered possible -- Consequent Production of Colors -- Action of Bodies mechanically strained or pressed -- Action of Sonorous Vibrations -- Action of Glass 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 Color and Polarization of Sky-light -- Generation of Artificial Skies.

§ 1. Action of Crystals on Polarized Light: the Nicol Prism.

     We have this evening to examine and illustrate the chromatic phenomena produced by the action of crystals, and double-refracting bodies generally, upon polarized light, and to apply the Undulatory Theory to their elucidation. For a long time investigators were compelled to employ plates of tourmaline for this purpose, and the progress they made with so defective a means of inquiry is astonishing. But these men had their hearts in their work, and were on this account enabled to extract great results from small instrumental appliances. For our present purpose we need far larger apparatus; and, happily, in these later times this need has