EASTING OF THE TRADE- WINDS, ETC. 151 



mass of this air is equivalent to a sea of mercury covering the earth 

 aroimd and over to the depth of 30 inches, and that this very sub- 

 tile mass is in a state of unstable equilibrium, and in perpetual com- 

 motion by reason of various and incessant distm'bing causes ; — 

 when we reflect farther upon the recent discoveries of Schwabe and 

 of Sabine concerning the spots on the sun and the magnetic ele- 

 ments of the earth, which show that if the sun or its spots be not 

 the great fomitain of magnetism, there is at least reason to suspect 

 a close alliance between solar and terrestrial magnetism ; — that 

 certain weU-known meteorological phenomena, as the aurora, come 

 also within the category of magnetic phenomena ; — that the mag- 

 netic 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 coinci- 

 dent mth either the terrestrial or with that which the direct solar ray 

 would indicate, but that it follows, and in its double curvatures con- 

 forms to the magnetic equator ; — moreover, vdien we reflect upon 

 Barlow's theory and Fox's observations, which go to show that 

 the direction of metallic veins of the northern hemisphere, Avhich 

 .generally lie north-east and south-westwardly, must have been in- 

 fluenced by the direction of the magnetic meridians of the earth or 

 vji ; — finally, I say, when we reflect upon magnetism in all its 

 aspects, we may well inquke whether such a mass of highly mag- 

 netic gas as that which surrounds our planet does not intervene, by 

 reason of its magnetism, in influencing the circulation of the atmo- 

 sphere and the com'se of the winds. 



318. This magnetic sea, as the atmosphere may be called, is con- 

 The needle in its di- tinuallv ae^itatod I it is disturbed in its movements by 



unial variations, the .«^."^^ i-i , ■ i i^ t i • 



barometer in its read- various mnuences wnicu prevcut it irom adjusting 

 sphere'in its^eteSrkai itsclf to any permanent magnetic or other dynamical 

 s^mriours foTtheir status ; and its para-magnetic properties are known 

 maxima and minima, to Vary with cvcry chaugo of pressm'o or of tempera- 

 tm^e. The experiments of Faraday show that the magnetic force 

 of the an* changes with temperature ; that it is least near the 

 equator, and greatest at the poles of maximum cold ; that it varies 

 with the seasons, and changes night and day ; nay, the atmosphere 

 has regular variations in its electrical conditions expressed daily at 

 stated hom's of maximum and mininum tension. Coincident with 

 this, and in aU parts of the world, but especially in sub-tropical 

 latitudes, the barometer also has its maxima and minima readings 

 for the day. So also, and at the same hours, the needle attains the 

 maxima and minima of its diurnal variations. Without other. 



