On Light (Volume 2) - Softcover

Book may have numerous typos, missing text, images, or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1885. Excerpt: ... LECTURE II. Rotation of the plane of polarization of polarized light produced by various liquids--Its application to quantitative determinations, and to the study of molecular grouping-- Magnetic rotation of the plane of polarization--Application to the discrimination between isomeric compounds-- Bright lines in the spectra of flames--Application as chemical tests--Discovery thereby of new elements-- Connexion between the powers of emission and absorption of the same substance for the same kind of Light-- Conditions as to temperature which determine whether a spectral line shall appear as bright or dark. I HAVE mentioned the rotation of the plane of polarization of polarized light as another property of light which has been turned to account in investigation. It was in the year 1815 that Biot, in pursuing his investigations of the colours developed in polarized light which is subsequently analysed, by the introduction of a crystalline plate which is variously inclined, being desirous of working with inclinations within the crystal greater than could be obtained when the plate is inclined in air, was led to try the effect of inclining the plate when immersed in oil of turpentine contained in a cell with parallel sides. The oil being of considerable refractive index, approaching that of plate glass, and accordingly that of ordinary minerals, would allow the passage of light within the crystal at an inclination higher than that attained at even a grazing incidence when the plate is in air. But in order to establish the legitimacy of the process it was necessary to show that the oil did not itself act on polarized light. Contrary to what was to have been anticipated, inasmuch as the oil is alike in all directions, differing notably in that respect from a crystal, the oil did act on pola...