Book Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1841 edition. Excerpt: ... LECTURE III. POLARIZATION OF LIGHT. Gentlemen, --Having examined the principal phenomena of polarized light, and their laws--so far as these laws can be detected by experiment--we may now proceed to consider their connexion with the physical theory. On a former occasion, when considering the phenomena of unpolarized light, I discussed their bearing upon the two theories--the theory of Newton and that of Huygens; and it appeared, on an examination of the facts then considered, that the weight of probability was altogether in favour of the latter. Of the phenomena which we have been lately considering, and of those which still remain to be unfolded, the explanations afforded by the Newtonian theory are, comparatively speaking, so scanty and incomplete, that we shall best consult our own progress in this interesting branch of science, by confining our attention in what follows to the wave-theory. It is strange that the department of optics in which the wave-theory now stands unrivalled, should be the very same which Newton selected as affording the most decisive evidence against it. "Are not," says he, "all hypotheses erroneous, in which light is supposed to consist in pressure, or motion, propagated through a fluid medium ?" . . . . "for pressures, or motions, propagated from a shining body through an uniform medium, must be on all sides alike; whereas it appears that the rays of light have different properties in their different sides." In this objection Newton seems to have had his thoughts fixed upon that species of undulatory propagation, whose laws he himself had so sagaciously unfolded. When sound is propagated through air, or water, or any other uniform medium, the vibrations of the particles of the air, or water, are performed in...