II. On the refraction-equivalents of the elements

Abstract

In our paper “On the Refraction, Dispersion, and Sensitiveness of Liquids,” Mr. Dale and I pointed out a property of bodies which we termed their “specific refractive energy.” It is the refractive index minus unity, divided by the density, or in symbolical language μ -1/ d . We found that this is a constant unaffected by temperature, and that the specific refractive energy of a mixture is the mean of the specific refractive energies of its constituents. At the same time, however, we admitted that in both cases our numbers were not in perfect accordance with theory, there being some unknown cause which affected them to a slight extent. These conclusions, both in regard to the general law and its qualification, have been since confirmed by continental physicists, and especially by the late rigorous experiments of Wullner. In the same paper we ventured also on the generalization that “every liquid has a specific refractive energy composed of the specific refractive energies of its component elements, modified by the manner of combination.” Later research has confirmed this also, extending it to conditions of matter other than liquid, and showing more clearly when such modifications occur, and what is their nature. Professor Landolt, of Bonn, has greatly advanced our knowledge of the subject, and has simplified the calculations by adopting what he terms the refraction-equivalent, that is, the specific refractive energy multiplied by the atomic weight, or P μ -1/ d . Recent investigations in fact tend to the general conclusion that the refraction-equivalent, not only of mixtures, but of every com­pound body, is the sum of the refraction-equivalents of the elements that compose it.