Six Lectures On Light

Relation of Theories to Experience -- Origin of the Notion of the Attraction of Gravitation -- Notion of Polarity, how generated -- Atomic Polarity -- Structural Arrangements due to Polarity -- Architecture of Crystals considered as an Introduction to their Action upon Light -- Notion of Atomic Polarity applied to Crystalline Structure -- Experimental Illustrations -- Crystallization of Water -- Expansion by Heat and by Cold -- Deportment of Water considered and explained -- Bearings of Crystallization on Optical Phenomena -- Refraction -- Double Refraction -- Polarization -- Action of Tourmaline -- Character of the Beams emergent from Iceland Spar -- Polarization by ordinary Refraction and Reflection -- Depolarization.

§ 1. Derivation of Theoretic Conceptions from Experience.

     One of the objects of our last lecture, and that not the least important, was to illustrate the manner in which scientific theories are formed. They, in the first place, take their rise in the desire of the mind to penetrate to the sources of phenomena. From its infinitesimal beginnings, in ages long past, this desire has grown and strengthened into an imperious demand of man's intellectual nature. It long ago prompted Cæsar to say that he would exchange his victories for a glimpse of the sources of the Nile; it wrought itself into the atomic theories of Lucretius; it impelled Darwin to those daring speculations which of late years have so agitated the public mind. But in no case, while