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 framing theories, does the imagination _create_ its
materials. It expands, diminishes, moulds, and refines, as the case