Six Lectures On Light

Origin of Physical Theories -- Scope of the Imagination -- Newton and the Emission Theory -- Verification of Physical Theories -- The Luminiferous Ether -- Wave-theory of Light -- Thomas Young -- Fresnel and Arago -- Conception of Wave-motion -- Interference of Waves -- Constitution of Sound-waves -- Analogies of Sound and Light -- Illustrations of Wave-motion -- Interference of Sound Waves -- Optical Illustrations -- Pitch and Color -- Lengths of the Waves of Light and Rates of Vibration of the Ether-particles -- Interference of Light -- Phenomena which first suggested the Undulatory Theory -- Boyle and Hooke -- The Colors of thin Plates -- The Soap-bubble -- Newton's Rings -- Theory of 'Fits' -- Its Explanation of the Rings -- Overthrow of the Theory -- Diffraction of Light -- Colors produced by Diffraction -- Colors of Mother-of-Pearl.

§ 1. Origin and Scope of Physical Theories.

     We might vary and extend our experiments on Light indefinitely, and they certainly would prove us to possess a wonderful mastery over the phenomena. But the vesture of the agent only would thus be revealed, not the agent itself. The human mind, however, is so constituted that it can never rest satisfied with this outward view of natural things. Brightness and freshness take possession of the mind when it is crossed by the light of principles, showing the facts of Nature to be organically connected.

     Let us, then, inquire what this thing is that we have been generating, reflecting, refracting and analyzing.