Academy of Sciences, August 16.—M. Emile Roux in the chair.—M. de Sparre: Remarks on the depressions resulting from a breakage in a water main under pressure.—Kyrille Popoff: The integration of the equations of ballistics under general conditions of resistance.—Pierre Auger and Francis Perrin: The shocks between a-particles andatomic nuclei. An application of a modification of C. T. R. Wilson's method of studying the paths of a-rays. Photographs of the paths were taken with two cameras at right angles to each other, and details of results in argon and in hydrogen are given. For argon the value of the atomic number calculated from the results of the observations is 19 (instead of 18).—I. Newton Kugelmass: A new apparatus, the nephelectrometer. The change in the transparency of a colloidal solution is measured by the deflection of a millivoltmeter connected with a thermocouple. The light from an electric lamp, after passing through a cell containing distilled water, is allowed to fall on the thermocouple for a fixed time, and the deflection of the millivoltmeter measured (I). The water is then replaced by the colloidal solution and the deflection (I') measured under the same conditions. The ratio I'/I gives the transparency index.—A. Marcelin: Measurement of the pressure of "superficial fluids."Detailed study of oleic acid.—F. Granel: The morphological signification of the pseudobranch of the teleosteans.