NATURE [Feb. 22, 187 2 wheels, relating to the reaction-wheel.-M. Saint-Venant communicated a note by M. Boussinesq on the eqµation of the partial derivatives of the velocities in a homogeneous and ductile solid undergoing deformation parallel to a plane.-M. Serret presented a note by M. de Tastes in reply to a recent note by M. Ciotti on the employment of vibrating elastic plates as a means of propulsion. M. de Tastes stated that the elastic plate propeller is his invention, communicated by

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... to M. E. Ciotti.-M. E. Dubois presented a reply to M. Ledieu's objections to the employment of the marine gyroscope.-M. Delaunay presented a note by M. C. Wolf on the reflecting power of mirrors of silvered glass, an,! their application to astronomical purposes.-A note by M. D. Genez on the absorption-bands produced in. the spectrum by solutions of hyponitrous, hypochlorous, and chlorous acid;, was communicated by M. H. Sainte-Claire Deville.-A note by M. Baudrimont on the recent experiments of M. Poey with regard to the influence of violet lignt upon vegetation was read, in which the author stated that he had arrived at totally different results, having found that violet light was fatal to vegetation. -A great number of communications from all parts of France, and also from Belgium, Switzerland, and Algeria, relating to the aurora of February 4, were laid before the Academy; they included notices of magnetic disturbances observed in the telegraphic lines.-M. Delaunay presented a paper by M. E. Stephan containing a list of nebulre discovered and observed at the Observatory of Marsei!les.-M. E. Vicaire