502 Geology and Magnetism. 



that the south pole of a magnet has a greater affinity for oxygen 

 than the north pole. The difference in the oxidation of the south 

 pole, compared with the north, is easily proved by various simple 

 methods. All that is required is to place the ends of a magnet in 

 water, and allow it to remain undisturbed for several days, and 

 the fact is soon proved. A very powerful horse-shoe magnet 

 will decompose water, and the oxidation will be observed to go 

 on at the south pole, and the evolution of the hydrogen at the north 

 pole : hence it is manifest that the currents move from the south 

 pole to the north of the needle: the magnet possesses the property 

 of filtering, as it were, the oxygen from the stream^ be that stream what 

 it may, such is the effect and such the direction of the current." 



Mr. Hopkins next refers to the reduction of metals by 

 electro-galvanic currents, by which he accounts for some 

 phenomena of metalliferous veins. Where metals are found 

 in the metallic state, it has been usual to ascribe their presence 

 under such circumstances to the action of heat, although we 

 frequently find them, particularly copper and silver, the ores 

 of which resist a very high temperature in a native state, 

 deposited on timber and decayed leaves in old mines, proving 

 the ordinary process of fusion to be incapable of accounting 

 for their reduction. Besides, it is found impossible for castings 

 to take the exact impression of the mould, owing to the 

 great heat required to give metals, even the most fusible, a 

 perfectly homogeneous consistence, as well from the lodg- 

 ment of air as other causes. In veins, however, we find 

 the native metals deposited in every crevice, presenting an 

 exact form of the mould, whether this consists of solid quartz 

 rock or soft clay, or substances more fusible than the metal 

 itself. 



We must therefore look for some other agency than that 

 of fire for such effects. Electro-magnetic currents are ad- 

 duced by Mr. Hopkins, and he reconciles many of the condi- 

 tions in which metals occur in veins, with effects produced 

 on metallic solutions by the galvanic battery. 



