LA LA HAUSSE BAISSE INDIQUE. INDIQUE. --------- --------- DES VENTS DE LA DES VENTS DE LA PARTIE DU PARTIE DU N.E. S.O. (DU N.O. a l'E) (DU S.E. a l'O.) (PAR LE NORD. ) (PAR LE SUD. ) DE LA DE SECHERESSE. L'HUMIDITE. --------- --------- UN VENT UN VENT PLUS FAIBLE PLUS FORT EXCEPTE S'IL PLEUT EXCEPTE S'IL PLEUT AVEC DE FORTES BRISES AVEC DE PETITES BRISES DU N.E. DU N.E. --------- --------- Mouvements lents, Le commencement Temps durable. de la hausse, --------- apres une grande Mouvements rapides, baisse presage Temps variable. un Vent violent. MARINE BAROMETERS. =19. The Common Form.=--The barometer is of great use to the mariner, who, by using it as a "weather glass," is enabled to foresee and prepare for sudden changes in the weather. For marine purposes, the lower portion of the glass tube of the barometer must be contracted to a fine bore, to prevent oscillation in the mercurial column, which would otherwise be occasioned by the movements of the ship. This tube is cemented to the cistern, which is made of boxwood, and has a moveable leathern bottom, for the purpose of rendering the instrument portable, by screwing up the mercury compactly in the tube. The tube is enclosed in a mahogany frame, which admits of a variety of style in shape, finish, and display, to meet the different fancies and means of purchasers. The frame is generally enlarged at the upper part to receive the scales and the attached thermometer, which are covered by plate glass. The cistern is encased in brass for protection, the bottom portion unscrewing to give access to the portable screw beneath the cistern. Figs. 13 and 14 illustrate this form of barometer. Marine barometers require to be suspended, so that they may remain in a vertical position under the changeable positions of a vessel at sea. To effect this they are suspended in gimbals by a brass arm. The gimbals consist of a loose ring fastened by thumb-screws to the middle part of the frame of the barometer, in front and back. The forked end of the arm supports this ring at the sides, also by the aid of thumb-screws. Hence the superior weight of the cistern end is always sufficient to cause the instrument to move on its bearing screws, so as always to maintain a perpendicular position; in fact, it is so delicately held that it yields to the slightest disturbance in any direction. The other end of the arm is