Page:Proceedings of the Royal Society of London Vol 60.djvu/155

140 This information is given in the preceding table (pp. 136—139), in which for the sake of completeness the lines obtained from eliasite are also shown.

In most of the experimental work connected with this research, I have been assisted by Mr. Shackleton, while Mr. Fowler is generally responsible for the determination of wave-lengths in the less refrangible part of the spectrum, and Mr. Baxandall for the reduction of the photographs.

This paper is. intended to give a preliminary account of some recent investigations into the specific refraction of the elements. It may be conveniently divided into two distinct parts. The first part is a revision and extension of the list of specific and atomic refractions, which was first published in the ‘ Phil. Trans.’ for 1870, and was reprinted with modifications in a lecture given at the Royal Institution in 1877. The second part is an amplification of some deductions made in that lecture.

The following table contains the atomic weights, the specific refractions, and the atomic refractions of the elements as revised and extended. For the atomic weights I have adopted the numbers recently published by the American Chemical Society’s Committee on Atomic Weights (‘ J. Amer. Chem. Soc.,’ vol. 17), revised up to January, 1894. In regard to the specific refraction, advantage has been taken of the work done in some departments of the inquiry by Landolt, Haagen, Briihl, Topsoe and Christiansen, Mascart, Becquerel, Kanonnikoff, Soret, Kasim, Ghira, Perrot, Tutton, Lord Rayleigh, Edwards, and others, as well as many additional observations made by myself or by Mr. Hibbert.

The atomic refraction is the product of the numbers in the two earlier columns, that is, it equals where P is the atomic weight, and p —ljd is the specific refraction, that is, the refractivity divided by the density. Of course, these are not generally determined by observations of the element itself, but are deduced from those of its salts or other compounds.