LONDON. Royal Society, April 6.—Sir Charles Sherrington, president, in the chair.—F. E. Smith: On an electromagnetic method for the measurement of the horizontal intensity of the earth's magnetic field. A Helmholtz-Gaugain arrangement of coils consisting of two interwoven helices of bare copper wire wound in spiral grooves in a marble cylinder are mounted on each side of the centre. Each coil is of 30 cm. radius, of six turns, and of if 11/2mm. pitch. The cylinder is mounted on a non-magnetic base, and can be rotated about a vertical axis. The magnet at the centre is i cm. long and about 6 sq. mm. in cross-section; it is supported on a V of aluminium foil by a fine quartz fibre, to which is attached a reflecting mirror and a damping vane. The magnet is easily removed from its support, and a copper wire of equal weight substituted. The axial magnetic field due to the current in the coils is made slightly greater than “H,” and its component in the magnetic meridian opposes H. By adjustment of the angle a between the axis of the cylinder and the direction of magnetic north, the indicator magnet is caused to set at right angles to the meridian. When torsion is eliminated, H =Fz cos a, where F is constant of coil system and i is current. A determination of H occupies less than 4 minutes. The probable error, including that due to uncertainty of the value of the current, measured by a current balance, is about + 4 in 100,000.—G. I. Taylor: Stability of a viscous liquid contained between two rotating cylinders. Steady motion of viscous liquid between two concentric rotating cylinders is unstable for symmetrical disturbances, provided the velocity of the system is greater than a certain value, and the ratio of angular velocities of the cylinders is less than the reciprocal of the square of the ratio of their radii, or is negative. The type of instability is periodic along the length of the cylinders, consisting of vortices enclosed in partitions rectangular in section, and they rotate alternately in opposite directions. When the cylinders rotate in the same direction each vortex extends across the space between the cylinders. The length occupied by each vortex is equal to the thickness of fluid between them. When the cylinders rotate in opposite directions, two systems of vortices rotating as though geared together appear. Some criteria for stability in approximate form suitable for numerical computation have been obtained.—T. H. Havelock: Dispersion formulas and the polarisation of scattered light; with application to hydrogen. Simple types of dispersion formulae are considered when the medium consists of anisotropic molecules distributed at random and having an axis of symmetry. A formula for the corresponding ratio of the intensities of the two polarised components of light scattered at right angles, when the primary light is unpolarised, is given. The case of hydrogen is examined numerically and the ratio of the intensities agrees substantially with Lord Rayleigh's experimental value.—G. R. Goldsbrough: The cause of Encke's division in Saturn's ring. A satellite will, from its inclined path alone, produce one new division in the ring system. If the satellite be Mimas, a narrow division closely corresponding to Encke's division is produced. Similarly, Enceladus should produce a division in Ring B, but it would be almost unobservable.—C. Spearman: Correlation between arrays in a table of correlations. Correlations between arrays are expressed as functions of the independent variable elements entering into the main variables. When only one element is common to any different variables, then the correlation between every two parallel arrays amounts to plus or minus unity. The converse is also true. The correlational coefficients considered are derived from product moments and the proofs do not assume any “normal” frequency distributions.—W. L. Balls: Apparatus for determining the standard deviation mechanically. The apparatus is related to the “Harp” Harmonic Analyser, similarly utilising separately loaded strings to deflect a yoke upon which they all converge. The design of the yoke has been modified to make the readings quantitative, and each string is loaded in proportion to the square of its deviation from the zero position. A template representing the frequency curve under examination is inserted behind the loaded strings, and the movement of an optical lever gives the “sum of the squares of the deviations.” The reading is then transferred to a monograph to complete the calculation. The values obtained are correct to within 5 per cent.