PREFACE. . Sothern - June 29,51 THE that any treatise which attempted to give a comprehensive account of all the various practical applications of Optics, in addition to the experimental and theoretical portions of the subject, would necessarily be of an exceedingly voluminous character. I have accordingly limited the present work to one special branch of Optics, and have endeavoured to place before the reader as concise a treatise upon the Mathematical Theory of Light, and such experimental phenomena as are immediately connected therewith, as the nature of the case will admit. Those who are acquainted with the Mathematical Theories of Hydrodynamics, Sound and Elasticity on the one hand, and of Electricity and Light on the other, cannot fail to have been struck with the difference, which exists between the two classes of | subjects. In the former class, certain equations are obtained, which approximately, though not quite accurately, specify in a mathematical form, the physical state of fluids and solids as they exist in Nature; and the subsequent investigation of these branches of Science, is thereby in great measure reduced to a question of mathematics. As soon as the fundamental equations are established, the subject is brought within the dominion of mathematical analysis, and mathematicians are enabled to exercise their ingenuity and analytical skill, in elaborating and developing the results which flow from them. But in the Theory of Light, we are confronted with a totally different state of things. Although the existence of the luminiferous ether may, at the present day, be regarded as a scientific axiom, which is as firmly established as any other scientific law, yet the properties of the ether are almost entirely unknown to us. |