LONDON. Royal Society, February 4.—Sir William Crookes, president, in the chair.—Prof. G. H. Bryan and R. Jones: Discontinuous fluid motion past a bent plane, with special reference to aeroplane problems. The present investigation is based on the theory of discontinuous fluid motion, and in particular on the recent developments of that subject by Sir G. Green- hill. Its object is to obtain a hydrodynamical estimate of the effects of camber on the lift and drift of a lamina moving through a fluid, the motion being two-dimensional, and regarding the lamina as an aerofoil. Instead of considering continuously curved laminæ, the investigation deals with lamine the front and rear portions of which are plane, but which meet at a dihedral angle. The method is applicable to surfaces with two or more bends. The general conclusions are in agreement with experimental results, that a moderate degree of camber is beneficial in increasing the lift without a corresponding increase in drift.—Prof. A. Fowler: A new type of series in the band spectrum associated with helium. The band spectrum associated with helium, as previously described by Curtis and Goldstein, includes bands with single heads and bands with double heads. A preliminary analysis of this spectrum has led to the following conclusions:—(i) The doublets do not follow the ordinary law of band spectra, but can be arranged in two series of the type hitherto exclusively associated with line spectra, and can be represented by the usual formuke involving the Rydberg constant. Nine bands of the main series, and four of the second fainter series, have been identified. (2) The two series may be likened to the principal and diffuse series in the case of line spectra, but the usual relation between such series is not certainly indicated, and no equivalent of the sharp series has yet been traced. (3) The doublet separations are not in accordance with those associated with line spectra; they diminish in passing along the series, but do not vanish at the limit. No regularity in the arrangement of the single bands has been recognised.—T. R. Merton: The spectra of ordinary lead and lead of radio-active origin. Wave-length measurements have been made of some of the principal spectrum lines of ordinary lead and the lead in pitchblende residues. It might reasonably be expected that small differences in the wave-lengths would be found, more especially in the case of any lines which belong to doublet or triplet series, since, according to the views of Prof. Hicks, an atomic weight termenters exactly into the separations of such doublets or triplets. No series have yet been discovered in the spectrum of lead, but it is probable that they exist, and an estimate of the order of the differences of wave-length to be expected, according to Prof. Hicks's views, is given. No differences of this order have been observed, the spectra taken in juxtaposition showing no differences of wave-length, whilst the wave-length measurements of seven of the most prominent lines in the two leads agree to 0.03 Å.U. A special comparison of the line λ4058 Å.U. with the interferometer shows that the wave-lengths of this line in the ordinary and radio-active lead are identical to within 0.003 Å.U.—A. O. Rankine: The viscosity of the vapour of iodine. The paper records the method used by the author for measuring the viscosity of iodine vapour at four different temperatures ranging from 124° C. to 247° C. The basis of the method is the distillation of iodine from one vessel to another through a narrow capillary tube, the temperature of which could be varied. One of the vessels contains solid iodine, and is raised to 100° C., thereby establishing the driving pressure. The other vessel is immersed in a freezing mixture, so that the iodine which is transpired as superheated vapour is condensed there, the mass so transpired being determined by weighing the vessel, which is removable. The method gives, in repeated experiments, very consistent results, and the values obtained may be taken as accurate to about ½ per cent. The range of temperature variation is not large enough to make the results suitable for testing the validity of Sutherlands formula, but it is found that they are, at any rate, not inconsistent with that formula.