Professor Draper, of New York, proved that the result is the same whether the incident light be polarized or not, and that the dispersed or degraded light is never polarized, but that it emanates in all directions, as if the substance were self-luminous; he made experiments with light from all parts of the solar spectrum, and with various substances, and always found that the refrangibility of the incident ray was diminished by internal dispersion, and that the colour was changed to suit the new refrangibility. Professor Draper has also shown that the law of action and reaction prevails in all the phenomena of the sunbeam, as in every other department of nature; so that a beam cannot be reflected, refracted, much less absorbed, without producing some change upon the recipient medium; and Mr. Power proved analytically that the solar rays can exercise no action upon any medium through which they are transmitted, without being accompanied by a diminution of refraction. He says, “The new light emanating from the fluorescent media is just like any other light of the same prismatic composition. In its physical properties it retains no trace of its parentage; it is of terrestrial origin, and its colour depends simply on its new refrangibility, having nothing to do with that of the producing rays, nor to the circumstance of their belonging to the visible or invisible part of the spectrum.” These phenomena can only be explained by the undulatory theory of light. SECTION XXIII. Objections to the Undulatory Theory, from a difference in the Action of Sound and Light under the same circumstances, removed—The Dispersion of Light according to the Undulatory Theory—Arago’s final proof that the Undulatory Theory is the Law of Nature.