I. “A Comparison of Platinum and Gas Thermometers, including a Determination of the Boiling Point of Sulphur on the Nitrogen Scale: an Account of Experiments made in the Laboratory of the Bureau International des Poids et Mesures, at Sèvres.” By Dr. P. Chappuis and Dr. J. A. Harker. Communicated by the Kew Observatory Committee. II. “A Preliminary Note on the Morphology and Distribution of the Organism found in the Tsetse Fly Disease.” By H. G. Plimmer and J. Rose Bradford, F. R. S. III. “The Colour Sensations in Terms of Luminosity.” By Captain Abney, C.B., R.E., F. R. S. IV. “On the Orientation of Greek Temples, being the Results of some Observations taken in Greece and Sicily, in May, 1898.” By E. C. Penrose, F. R. S. V. “The Absorption of Rontgen Rays by Aqueous Solutions of Metallic Salts.” By Lord Blythswood and E. W. Marchant. Communicated by Lord Kelvin, F. R. S. VI. “On the Oxidation of Carbon at ordinary Temperatures by means of Atmospheric Oxygen with the Production of Electrical Energy.” By W. E. Case. Communicated by Sir William Preece, F. R. S. VII. “The Conductivity of Heat Insulators.” By C. G. Lamb and W. G. Wilson. Communicated by Professor Ewing, F. R. S. VIII. “On Simultaneous Partial Differential Equations and Systems of Pfaffians.” By A. C. Dixon. Communicated by Dr. J. W. L. Glaisher, F. R. S. IX. “On the Comparative Efficiency as Condensation Nuclei of Positively and Negatively charged Ions.” By C. T. R. Wilson. Communicated by the Meteorological Council. X. “Data for the Problem of Evolution in Man. II. A First Study of the Inheritance of Longevity and the Selective Death-rate in Man.” By Miss Mary Beeton and Professor Karl Pearson, F. R. S. XI. “Collimator Magnets and the Determination of the Earth’s Horizontal Magnetic Force.” By Dr. C. Chree, F. R. S. XII. “On the Resistance to Torsion of certain Forms of Shafting, with special Beference to the Effect of Iveyways.” By L. N. G. Filon. Communicated by Professor M. J. M. Hill, F. R. S. XIII. “On the Waters of the Salt Lake of Urmi.” By R. T. Gunther and J. J. Manley. Communicated by Sir John Murray, K.C.B., F. R. S. XIV. “On the Application of Fourier’s Double Integrals to Optical Problems.” By Charles Godfrey. Communicated by Professor J. J. Thomson, F. R. S. XV. “On Diselectrification produced by Magnetism. Preliminary Note.” By C. E. S. Phillips. Communicated by Sir William Crookes, F. R. S. XVI. “On the Orbit of the Part of the Leonid Stream which the Earth encountered on 1898, November 15.” By Dr. A. A. Rambaut. Communicated by Dr. G. J. Stoney, F. R. S. XVII. “On the Numerical Computation of the Functions G<sub>0</sub>(<italic>x</italic>), G<sub>1</sub>(<italic>x</italic>), and J<sub>n</sub>(<italic>x</italic> /<italic>i</italic>); and on the Boots of the Equation K<sub>n</sub>(<italic>x</italic>) = 0.” By W. Steadman Aldis. Communicated by Professor J. J. Thomson, F. R. S. XVIII. “Kesearches in Absolute Mercurial Thermometry.” By (the late) S. A. Sworn. Communicated by Professor H. B. Dixon, F. R. S.