LONDON. Royal Society, April 30.—A. E. H. Tutton: Determination of the yard in wave-lengths of light. The author has carried out a determination of the number of wave-lengths of the red light radiations of hydrogen (Ha) and cadmium (Cdr), and of the yellow radiations of neon (Nec), in the British Imperial Standard Yard, by an original method. The Imperial Standard Yard, at the official temperature 62° Fahrenheit and 760 mm. barometric pressure, is found to comprise 1,420,210.3 wave-lengths of the standard red lines of cadmium, Cdr, 1,562,408.6 wave-lengths of the yellow neon line Nec, and 1,393,266.5 wave-lengths of the red hydrogen line Ha. Instead of relying on direct determinations with cadmium light, to produce which the vacuum tube has to be heated to 340° C., which was found gravely to affect the thermal equilibrium and thereby the accuracy of the observations, the direct determinations with Ha (which is very close to Cdr) and Nec were used to calculate the value for Cdr; the two independent values thus obtained for Cdr were 1,420,210.8 and 1,420,209.8, an agreement which gives every confidence that the round number 1,420,210 is very near the truth. It is suggested that this round number might be taken as the length of the British yard.—U. R. Evans, L. C. Bannister, and S. C. Britton: The velocity of corrosion from the electrochemical standpoint. By excluding oxygen from the anodic areas, it has been found possible to tap and measure the whole of the electric current responsible for the corrosion of iron, and to show that the whole attack is of an electrochemical character. The current can never exceed that limiting value which would cause so much polarisation as to make the cathodic and anodic potentials equal; such ‘equipotential’ conditions are closely approached at high salt concentrations. Most of the polarisation occurs at the cathodic area. The law governing the ratio of anodic and cathodic areas is that the anodic area extends until the cathodic current density reaches the ‘protective value’ requisite to prevent further extension.—T. L. Eckersley: On the connexion between the ray theory of electric waves and dynamics. There is a very close analogy between the analytical description of the transmission of such electromagnetic waves and Schrödinger's wave theory of quantum dynamics. Optical ray methods are often used in the analysis of wireless wave transmission and the rays can be given a dynamical interpretation as the orbits of a group of waves (considered as a particle). The approximate ray method of analysis bears the same relationship to the true wave method that the Newtonian dynamics bears to the new wave mechanics. The theory can be applied to the transmission of waves between the earth and Heaviside layer, and approximate solutions obtained which, in the particular case of a well-defined conducting layer, give G. N. Watson's value of the attenuation coefficient. The solutions, like the older Bohr-Sommerfeld quantum solution, are incomplete, giving the direction cosines and attenuation coefficients, but not the amplitudes. The method, however, can be applied to a wide variety of cases.—Lord Rayleigh: On a night sky of exceptional brightness, and on the distinction between the polar aurora and the night sky. An exceptionally bright night sky on Nov. 8, 1929, is described, with photometric observations. It was of about four times the ordinary brightness and eight times the minimum ever observed. It was of the same chromatic constitution as usual, and the aurora line was not conspicuous. There was no accompanying magnetic disturbance. Spectra of the aurora and of the normal night sky are reproduced for comparison. Nitrogen bands are absent in the latter. Two unidentified bright lines in the night sky spectrum are remeasured. The wave-lengths found are 4419 and 4168.—T. H. Havelock: The wave resistance of a spheroid. It is shown how to calculate the wave resistance of an ellipsoid submerged in water and moving horizontally in any orientation. Explicit results are given for prolate and oblate spheroids moving in the direction of the axis of symmetry and at right angles to that axis.—O. W. Richardson and P. M. Davidson: The spectrum of H2. The bands ending in 2p 311 levels. The bands of the H2 spectrum are described which start on the levels 3d3,llab, 3d 3△ab, 4d3σ, 4d3llab, 4d3△ba and end in 2p3llab. The upper levels show pronounced uncoupling phenomena, and their properties are otherwise similar to those of the corresponding singlet levels of H2 and also to those of the d3∑, d3II, and d3△ levels of He2. The 3d3∑2p3II bands show a strong Zeeman response, just as do the 3d1∑2pi11∑ bands. The constants of the final ∏ levels, common to all the bands, are in good agreement with the supposition that this is the continuation at n = 2 of the upper levels of the a, p, λ bands for which n = 3, 4, and 5.—C. M. M'Dowell and F. L. Usher. Viscosity and rigidity in suspensions of fine particles (1, 2). In lyophobic suspensions of charged particles in an aqueous liquid, variation of viscosity with rate of shear is dependent on the formation of aggregates, whilst rigidity depends on the linking of the aggregates to form a continuous structure. Measurements of rigidity and of viscosity in relation to rate of shear were also made in suspensions of uncharged particles in inert organic liquids of the same density as the solid, in conjunction with microscopic observations. Photomicrographs show the existence of aggregates and structures or their absence, accordingly as the suspensions exhibit or fail to exhibit variable viscosity and rigidity.