1. The oscillations of a viscous wire exhibiting set are simple harmonic with regard to the position of set throughout the whole range of the in-motion and a considerable part of the out-motion. In the remainder of the out-motion the deviation from the simple harmonic condition is great.

2. The period of in-motion to the zero is distinctly greater than that of the out-motion from it.

3. A theoretical deduction of these results, and of the law of loss of energy per oscillation, can be founded on the assumption that that loss is due to the rupture of strained molecular (which may be finite crystalline) groups.

4. A sudden change in the oscillation parameters when the decreasing maxima pass through a definite magnitude is explainable by the existence of a dominant type of groups which cease to rupture when the decreasing strain reaches a definite value; and the known peculiar temperature and stress effects are explainable as depending on well-recognised conditions of structural changes.

It has been pointed out by several experimenters, notably by Ewing, and Gray and Ross, that a specimen of steel freshly annealed is in a peculiar magnetic condition. Thus, if a specimen, thoroughly demagnetised, is annealed and then tested, a certain I–H curve is obtained. If it be then demagnetised, and tested again, a second I–H curve is obtained which lies definitely below the first; and any further tests after demagnetisation produce a repetition of the second curve, which is characteristic of the specimen. To obtain the first curve again, the specimen has to be annealed from the same temperature as before, and a test made before demagnetisation.

First of all there is discussed the best method of obtaining an intense beam of parallel rays having each ray of equal brightness, as the production of such a beam is a pre-requisite of all spectrophotometric measurements of light absorption. Next there are briefly described three new types of “flicker“ spectrophotometer, the first of these depending on polarisation, the second on refraction, and the third on reflection. All three are quite successful: which it is best to use depends on the circumstances of the case. Finally, three general governing principles are laid down which would seem to apply equally to all types of flicker photometer.

There remains the pleasant duty of expressing my thanks to the Trustees of the Carnegie Trust for the various grants which have made these somewhat expensive investigations possible.

The present paper describes a number of experiments made in connection with Christiansen's experiment in which a beam of light is passed through a transparent insoluble powder immersed in a liquid, with the result that light of the particular colour for which the indices of powder and liquid are the same passes unaffected, while light of all other colours is scattered. In this communication only the simplest case of the above is dealt with, that, namely, in which a flat piece of glass, ground on one side, takes the place of the powder, the rugosities of the ground surface representing a single layer of grains, and air takes the place of the liquid. In such a case there is, of course, no colour of light for which the indices of solid and liquid are alike, and indeed it was found that the colour of the light made very little difference to the results. On the other hand, however, it soon became apparent that different ways of grinding the glass surface led to very different effects. Accordingly, as no previous work appears to have been done in this field, and as it seemed a promising one, it was decided to make a systematic study of the various cases. Each specimen of glass employed was photomicrographed, and had its polar light distribution measured by a photometer. Two methods of characterising the particular scattering power of a screen soon suggested themselves and have been formally defined—the one connected with the Angle of Maximum Total Emission, and the other with the Equivalent Cavity.

It is hoped to continue the investigation not only on the above lines, but also in the direction of ascertaining the effect of a number of plates, i.e. of successive layers of light-scattering particles; and in investigating the polarisation effects, which some rough preliminary experiments have shown to be marked.

I am glad of this opportunity of acknowledging the help I have received from the Trustees of the Carnegie Trust in the form of grants for the construction of the special apparatus necessary; and desire to tender my grateful thanks to Professor MacGregor for the many facilities for carrying on the work which he kindly placed at my disposal.

The experiments to be described in this communication were undertaken with the purpose of obtaining values of the compressibility of certain salts, the volume of dilute solutions of which is less than the volume of the constituent water. The densities of such solutions, chiefly hydroxides, sulphates, and carbonates, are discussed by MacGregor in a series of papers published in the Transactions of the Royal Society of Canada; and Kohlrausch includes several of them in his paper on the density of dilute solutions.

(1) It has been shown that in the case of plane strain the stresses in a body can be obtained from a single stress function χ satisfying

where

Solutions of equation (1) will be applied to obtain the stresses in an infinitely long wedge-shaped cylinder, having normal force varying according to some integral power of the distance from the angle applied to the plane faces, and the same at all corresponding points along the length of the cylinder.

Among about a hundred specimens of Daphnia pulex (De Geer) obtained for class purposes, at the end of May, 1912, I found two females in each of which the antennule of one side resembled that of a male. These cases seem worthy of notice in view of the paucity of existing records of similar abnormalities in Daphnia.

Previous Records of Abnormalities of the Antennules in Cladocera.

Kurz found, in October, 1873, an example of D. pulex in which the right antennule was short, as in the female, while the left approached in form that of the male, though it was not quite as large as the latter.

§ 1. In this paper are given the results of calculations made from continuous records of atmospheric electric potential obtained during the year 1912 at the Physical Laboratory of the University of Edinburgh.

During the summer of 1909 intermittent observations of the atmospheric electric potential and earth-air current were made at various points in Edinburgh, the results of which have already been communicated to this Society, and since October 1911 there has been an electrograph in operation at the laboratory.