The influence of atomic arrangement on refractive index

Abstract

1. The Mutual Electrostatic Influence of Doublets a Polarized Medium . The molecular refractivity of a compound is defined by the Lorenz-Lorent formula R = M / ρ n 2 – 1 / n 2 + 2 (1) where M is the molecular weight of the compound, and ρ its density when in a form for which the refractive index is n . The refractivity, defined in this way, is in many cases very nearly the same for different states of aggregation of the substance (liquid and vapour). Further, it is found that the molecular refractivity may be calculated by adding together constants termed "atomic refractivities” characteristic of the atoms in the molecule. This latter additive law is in general only approximately obeyed, and in many cases i breaks down entirely. In the electron theory of dielectric media, it is supposed that each atom under the influence of a steady electric field, is polarized. Its positive and negative parts are displayed relatively to each other, and in this way a field is cated around the atom which is equivalent to that of an electrical doublet where moment se is proportional to the strength of the exciting field. The veage electric force Ē inside the medium, the total polarization P per unit volme containing N atoms of one kind, and the dielectric constant K, are conected by the formula : Ē (K – 1) = P = ΣN se . (2) individual atom in the medium is influenced by an electrical field which is imposed of two parts. The first of these is the average field Ē. The nd is due to the effect on it of the surrounding polarized atoms, and is proportional to P. Lorentz has shown that, in certain special cases, the second is equal to ⅓ P; this occurs, for instance, when the surrounding atoms has a random distribution. The polarizing field is then (Ē + ⅓ P), and we suppose that it creates a doublet of strength (Ē + ⅓ P) e 2 λ where λ is constant characteristic of the atom. From this and from equation (2) it follows that M/ ρ · K – 1/K – 2 = a (⅓ N 0 e 2 λ 1 ) + b (⅓ N 0 e 2 λ 2 ) + . . . . (3) In this formula, N 0 is the number of molecules in a gram molecule, and there " a " atoms of the first kind, " b " of the second kind, and so on, in the Molecule of the substance.