391-393. Equations of the electromagnetic field 394. General equations of electric displacement for a doubly-refracting 395. Equations of magnetic induction 396. The disturbance which produces light, is represented by the electric 432-434. Plane of incidence perpendicular to the plane of symmetry 435-436. In this case, the direction of polarization is reversed by 462. Experiments on reflection from an electrified conductor are needed 463-464. Kundt's experiments on reflection from nickel and cobalt 465-466. Experiments on the transmission of light through thin films of 472. Table of the values of Hall's effect for different metals CHAPTER I. INTRODUCTION. 1. THE Science of Optics may be divided into the following four distinct branches :-(i) Geometrical Optics, whose object is to investigate the laws relating to the reflection and refraction of light, and the theory of optical instruments; (ii). Experimental Optics, whose object is to discover the optical properties of transparent and other substances, which are capable of affecting light; (iii) Physical Optics, whose aim is to explain optical phenomena by means of a dynamical theory; (iv) Physiological Optics, which deals with the sensation produced by light upon the retina of the eye. The present treatise will be principally confined to the third branch of the subject; but inasmuch as the fundamental object of every theory of light is to explain experimental facts by means of dynamical principles, it will be necessary to describe and discuss a variety of experimental phenomena, in order that we may be in a position to compare the results furnished by theory, with those established by experiment. 2. Two theories of light have been proposed, which are of a totally different character; viz. the Corpuscular Theory and the Undulatory Theory. The corpuscular theory was proposed by Newton, and it assumes that a luminous body emits material particles in all directions, which, by their impact upon the retina, produce the sensation of light. By the aid of this theory, Newton succeeded in explaining the linear propagation, and also the reflection of light; but amongst other imperfections, the theory leads to the conclusion, that the velocity of light in highly refracting substances is greater than in substances of less refractive power, whereas it can be proved by experiment that the exact 1 B. 0. |