LONDON. Royal Seciety, June 23.—Prof. C. S. Sherrington, president, in the chair.—E. F. Armstrong and T. P. Hilditch: A study of catalytic actions at solid surfaces. VI.—Surface area and specific nature of a catalyst: two independent factors controlling the resultant activity. The influence of the surface area of a nickel catalyst on its activity has been traced by examination of the bulk gravity of various types of catalyst: the most efficient catalyst occupies the greatest volume per unit mass. The rate of reduction in hydrogen of nickel oxide prepared in various ways has been examined at various temperatures, A light nickel oxide prepared from the precipitated hydroxide gave curves (hydrogen consumption/time) showing faint points of inflexion, which varied with the temperature of reduction; dense, fused nickel oxide gave a smoother curve, and nickel hydroxide deposited on kieselguhr as a support showed a smooth, continuous curve. The reduction curves are related to the physical conditions rather than to the formation of any definite compounds. When a support (kieselguhr) is overloaded with nickel hydroxide and reduced so that varying proportions of the nickel are in the metallic state, catalytic activity increases rapidly to a maxijmum, which is maintained until all the nickel hydroxide has been reduced to the elementary state. Catalytic activity is dominated by the condition of the surface layer of reduced nickel.—Sir J. B. Henderson: (i) A contribution to the thermodynamical theory of explosions; (ii) with Prof. H. R. Hasse. Advances in chemical thermodynamics, dealing with dissociation of gases and variation of their specific heats with temperature, are applied to the science of internal ballistics. Direct experiments on specific heats of gases are limited to temperatures below 1500° C., and extrapolation, based upon thermodynamic theory and extending to temperatures of 3500° C. and to pressures of 20 tons per sq. in., tests the theory severely. Part (i) contains the application of these theories to the calculation of the explosion-pressure of cordite in closed vessels, and the calculation of the curve of adiabatic expansion of the products of explosion bv considering a series of states of equilibrium and, following thereon, the ideal indicator diagram of a gun. In part (ii) the curve of rise of pressure and the maximum pressure allowing for burning of cordite in parallel layers and for varying capacity of chamber during burning, due to movement of the projectile, are calculated. The results enable the indicator diagram of gun, maximum pressure, and muzzle velocity of projectile to be calculated accurately from the chemical composition of explosive used and rate of burning of the cords. They also show the effects produced by variations in initial pressure, density of loading, temperature of charge, diameter of cords, etc. The method is also applicable to internal-explosion engines using gas or oil.—S. Bntterworth: Eddy current losses in cylindrical conductors, with special applications to the alternating current resistances of short coils. A general series for the eddy current losses produced in a non-magnetic metallic cylinder when placed in a transverse field of any form is developed. The theorv gives an approximate solution of the problem of the effective resistance of two equal parallel wires carrying equal currents either in the same or in opposite directions. The “uniform field” theory is applied to determine the effective resistance of parallel wire systems, and, by calculating the mean square field acting throughout the section of the coil, formulas are obtained for the effective resistances of single- and multi-layer sole noidal coils of either solid or stranded wire. Conditions producing the maximum value of L/R' for a given length of wire of given diameter are deduced. The observed inferiority of stranded wire coils as compared with solid wire coils at high frequencies is due to the lack of internal spacing of the strands oof the coils making the best conditions unattainable.—E. S. Bieler: The currents induced in a cable by the passage of a mass of magnetic material over it. The mass used is in the form of a spherical shell, and the deflection of a critically damped galvanometer in series with the cable is deduced. The results agree with those of experiments carried out in the laboratory on a small scale. The theoretical results are used to determine the law of variation of the galvanometer with different factors, and the relation between the galvanometer deflection and the E.M.F. which produces it.—Dr. G. Barlow and Dr. H. B. Keene: The experimental analysis of sound in air and water: some experiments towards a sound spectrum. The original sound vibration gives rise to an electric current of telephonic magnitude, which is analysed by a method of periodic interruption. A motor-driven interrupter with a range of interruption frequency from 3-2000/sec. is placed in series with a Broea galvanometer in the circuit containing the alternating current to be analysed. The speed of the interrupter is then slowly varied. When the interruptions synchronise with any component of the current, the galvanometer gives a steady deflection, the magnitude of which depends on the phase difference. Thus the amplitude of each component may be determined, and at the same instant the corresponding frequency is observed strobo-scopically. Experiments were made (1) to test the trustworthiness of the method by analysing alternating currents containing known constituents; (2) to analyse different types of sound in air, using both carbon microphone and magnetophone receivers; (3) to analyse sounds in water. The variations of the sound spectrum with distance, depth, and direction are investigated, and the spectrum of a motor-driven boat is obtained under various conditions.—Dr. G. Barlow; The theory of the analysis of an electric current by periodic interruption. A mathematical treatment of the method of periodic interruption used in the experimental analysis of sounds described in the previous paper is given, with an explanation of the effects of periodic interruption on the intensity and quality of osounds heard in a telephone.