LONDON Physical Society, June 15.—R. L. SMITH-ROSE and J. S. MCPETRIE: Measurement of the electrical constants of soil by a Lecher-wire method at a wavelength of 1-5 m. A parallel Lecher-wire system was set up and coupled to a source of oscillations of the desired frequency. The length of the stationary waves set up on the wires in air was measured and compared with the corresponding wave-length when the wires were immersed in the sample of soil under examination. The ratio of these wave-lengths gives directly a quantity involving both the conductivity and the dielectric constant of the soil. For conditions of normal moisture content the dielectric constant is 10 or 12, while the conductivity lies within the range 10-28 × 108 E.S.T.J. J. S. MCPETBIE:—A determination of the electrical constants of the earth's surface at wave-lengths of 1-5 and 0-46 m. The most sensitive condition for finding the electrical constants of a substance from a study of its reflecting properties for electromagnetic waves is obtained when the radiation is incident normally on the reflector. The experiments described show that in this case the reflection coefficient of copper gauze is practically unity at both wave-lengths. There appears to be little difference in the reflecting properties of ordinary soil and soil covered by grass, probably because the bulk of the reflection takes place at a small distance below the surface.—O. DABBYSHIBE: (1) A spectrometer determination of the metrical thickness and dispersive power of a thin film. By counting the numbers of EdserButler and Talbot bands produced within the same spectral range by a thin film of glass and a prism spectrometer, the metrical thickness of the film can be determined. The refractive index of the film for light of any standard wave-length can then be calculated from a count of the number of Talbot bands passing the position of the corresponding line in the spectrum as the Talbot echelon is rotated about the vertical edge of the film through an accurately measured angle. Two spectrometers are used in conjunction as a double-table spectrometer, and the other apparatus required is of the usual student-laboratory type. (2) Application of the theory of the transmitting echelon to the explanation of Talbot's and Powell's bands. On the basis of the theory of the transmitting echelon, the formation and the asymmetrical character of Talbot's bands, which are produced when a plate and aperture are placed in certain positions in the beam of a prism spectroscope, are explained analytically and represented diagrammatically. R. W. POWELL:—The thermal and electrical conductivity of metals and alloys: (1) Iron from 0° to 800° C. A longitudinal-flow method has been used to determine the thermal conductivity, at mean temperatures ranging from 30° to 800° C., of a nickel-plated rod of Armco iron containing approximately 99-92 per cent of iron. After allowance for the effect of the nickel plating, and extrapolation to 0° C., a value of 0-177 C.G.S. units is obtained for the thermal conductivity of the iron. This value is higher than that usually attributed to iron, but a chemically prepared iron of greater purity has been examined also and found to have a thermal conductivity of 0-194 C.G.S. units at 0° C.