Bulletin de l'Académie Royale de Belgique, No. 1.—Is the declination indicated by a compass independent of its magnetic moment? by Ch. Lagrange. According to Gauss's theory it may be assumed that the magnetic axis of a magnet lies in the direction of the lines of force of the field, whatever its magnetic moment may be. But in practice it is found that the orientation of a magnet depends upon the strength of its magnetisation. Since these systematic differences are not due to magnetic force, they must be due to some other force, probably a force hitherto unknown. Hence the magnetic chart of the earth calculated by Gauss's theory cannot be considered rigidly correct. A new constant must be introduced, depending upon the declinometer. The author foreshadows an explanation of these facts, based upon the “circulation of the ether,” and intimately associated with the physics of the globe.—Double decompositions of vapours, by Henryk Arctowsky. It is not necessary that two substances should be dissolved in water to bring about their mutual decomposition; or their “ionisation,” in terms of the electrolytic theory, is not altogether dependent upon water. Freshly sublimated mercuric chloride and flowers of sulphur were placed in small vessels inside a Bohemian glass tube over an organic combustion furnace. A current of pure dry hydrogen was introduced, which on heating formed sulphuretted hydrogen with the sulphur. This gas and the vapour of HgCl2 gave a precipitate of mercuric sulphide on the walls of the tube. This reaction, which is contrary to Berthelot's principle of maximum work, does not take more time than the corresponding reaction in water. To prove that it was a true double decomposition, CO2 was substituted for the hydrogen, when it was found that the sulphur vapour alone was unable to attack the mercuric chloride.