500 Geology and Magnetism. 



change in the density or property of the currents, and not from 

 any changes in their directions. That there is magnetic matter 

 in the atmosphere is indubitable, and that this matter is constantly 

 acted upon by the currents cannot be doubted. However, it must 

 not be expected that the variations are alike at all places, because 

 the disturbances in the equilibrium of the magnetic currents are 

 influenced by various causes of a local nature. Resembling the 

 weather in this respect, these variations may differ at different places 

 at the same instant of time. 



The next point to be considered is the direction in which the 

 magnetic currents move. If the currents, as we have previously 

 stated, emanate from the south pole of the earth and enter into 

 the north pole, we should expect somewhat different appearances in 

 the south aurora compared with the north ; because from the former 

 they rise from an aqueous element, which must produce a visible 

 portion of vapour ; and if so, the aurora will have the appearance 

 of steam; whereas in the latter, as the currents descend from an 

 aerial element, and are exposed to the effects of the sun, they must 

 be drier. This difference has been observed by several navigators. 



The southern aurora consists of long columns of clear white light, 

 shooting up from the horizon, and gradually spreading over the 

 whole sky. These columns are bent sideways at their upper ex- 

 tremities, and are in every respect similar to the northern lights, 

 except in being always of a whitish colour, whereas the northern 

 lights assume various tints, especially those of fiery and purple hue. 

 The figure is identical — indeed exactly such as would be produced 

 by the convergence, or vice versd, of the magnetic currents : and the 

 difference in the colours is precisely what we should have been led 

 to expect from the different nature of each pole. The saturated or 

 hydrogenous nature of the currents coming from the south pole 

 towards the north, will account for the observed peculiarity of the 

 southern hemisphere in its general temperature, moisture, rains, the 

 growth of vegetation, &c, as compared with that of the northern. 



The great ocean of air which envelopes the planet we inhabit, 

 and to which we are every instant beholden for supplying us with 

 the elements of vitality, is governed by the magnetic currents. 

 Whatever substances may be decomposed and converted into gases 





