Six Lectures On Light

Range of Vision not commensurate with Range of Radiation -- The Ultra-violet Rays -- Fluorescence -- The rendering of invisible Rays visible -- Vision not the only Sense appealed to by the Solar and Electric Beam -- Heat of Beam -- Combustion by Total Beam at the Foci of Mirrors and Lenses -- Combustion through Ice-lens -- Ignition of Diamond -- Search for the Rays here effective -- Sir William Herschel's Discovery of dark Solar Rays -- Invisible Rays the Basis of the Visible -- Detachment by a Ray-filter of the Invisible Rays from the Visible -- Combustion at Dark Foci -- Conversion of Heat-rays into Light-rays -- Calorescence -- Part played in Nature by Dark Rays -- Identity of Light and Radiant Heat -- Invisible Images -- Reflection, Refraction, Plane Polarization, Depolarization, Circular Polarization, Double Refraction, and Magnetization of Radiant Heat

§ 1. Range of Vision and of Radiation.

     The first question that we have to consider tonight is this: Is the eye, as an organ of vision, commensurate with the whole range of solar radiation -- is it capable of receiving visual impressions from all the rays emitted by the sun? The answer is negative. If we allowed ourselves to accept for a moment that notion of gradual growth, amelioration, and ascension, implied by the term evolution, we might fairly conclude that there are stores of visual impressions awaiting man, far greater than those now in his possession. Ritter discovered in 1801 that beyond the extreme violet of the spectrum there is a vast efflux of rays which are totally useless as regards our present powers of vision. These