Page:On the Determination of the Index of Refraction of Glass for the the Electric Ray.djvu/1

Rh Hoitsema has shown that Troost and Hautefeuille's deduction that a compound exists having the formula Pd2H is not warranted. The constancy of the heat of occlusion over the whole range of absorption is also opposed to the view that such a compound is formed.

The composition of fully charged palladium hydrogen corresponds closely with the formula Pd3H2 first suggested by Dewar. The principal and almost only evidence, up to the present, in favour of the formation of such a definite chemical compound is to be found in the approximation of the above atomic ratios to the theoretical value 1·5, required by the formula Pd3H2. Although Hoitsema’s arguments may be equally well directed against the existence of this compound, the authors consider that additional and independent evidence is desirable, and hope to be able to provide it.

It is also shown that the heats of occlusion of hydrogen in platinum and palladium black are not in favour of the view which has sometimes been put forward that the heat of occlusion of a gas represents the heat of condensation or liquefaction of the gas in the capillary pores of the absorbing substance, or the heat of solidification or fusion.

 "On the Determination of the Indices of Refraction of various Substances for the Electric Ray. II. Index of Refraction of Glass." By, M.A., D.Sc., Professor of Physical Science, Presidency College, Calcutta. Communicated by, F.R.S. Received October 1,—Read November 25, 1897.

In my previous paper, read before the Royal Society on October 20, 1895, I described a method of determining the indices of refraction of various substances for electric radiation, the principle of which depends on the determination of the critical angle at which total reflection takes place. A semi-cylinder of the given substance was taken, and the angle of incidence gradually increased till the rays were totally reflected. The experiment was repeated with two semi-cylinders, separated by a parallel air-space. The advantage of the latter arrangement was that the image cast by the two semi-cylinders remained fixed. The image underwent extinction when the angle of incidence attained the critical value.

The determination of the indices of refraction for long electric waves derives additional interest from Maxwell's theoretical relation between the dielectric constant and the refractive index for infinitely long waves. The relation K=μ2 has, however, been found to be fulfilled in only a few instances. The value ν∞ is usually deduced  VOL. LXII.