Page:Physical Geography of the Sea and its Meteorology.djvu/183

 Rh these minute bits of ferruginous dust that arrange themselves in lines and curves about magnets; when we reflect that this great magnet, the earth, is surrounded by a para-magnetic gas, to the molecules of which the finest atom from the file is in comparison gross and ponderous matter;—that the entire mass of this air is equivalent to a sea of mercury covering the earth around and over to the depth of 30 inches, and that this very subtle mass is in a state of unstable equilibrium, and in perpetual commotion by reason of various and incessant disturbing causes;—when we reflect farther upon the recent discoveries of Schwabe and of Sabine concerning the spots on the sun and the magnetic elements of the earth, which show that if the sun or its spots be not the great fountain of magnetism, there is at least reason to suspect a close alliance between solar and terrestrial magnetism—that certain well-known meteorological phenomena, as the aurora, come also within the category of magnetic phenomena;—that the magnetic poles of the earth and the poles of maximum cold are at or near the same spot;—that the thermal equator is not parallel to or coincident with either the terrestrial or with that which the direct solar ray would indicate, but that it follows, and in its double curvatures conforms to the magnetic equator;—moreover, when we reflect upon Barlow's theory and Fox's observations, which go to show that the direction of metallic veins of the northern hemisphere, which generally lie north-east and south-westwardly, must have been influenced by the direction of the magnetic meridians of the earth or air;—finally, I say, when we reflect upon magnetism in all its aspects, we may well inquire whether such a mass of highly magnetic gas as that which surrounds our planet does not intervene, by reason of its magnetism, in influencing the circulation of the atmosphere and the course of the winds.

348. The needle in its diurnal variations, the barometer in its readings, and the atmosphere in its electrical tension, all have the same hours for their maxima and minima. — This magnetic sea, as the atmosphere may be called, is continually agitated; it is disturbed in its movements by various influences which prevent it from adjusting itself to any permanent magnetic or other dynamical status; and its para-magnetic properties are known to vary with every change of pressure or of temperature. The experiments of Faraday show that the magnetic force of the air changes with temperature; that it is least near the equator, and