17 



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. 



Having so far shown that the magnetic and galvanic currents 

 are identical, differing only in the degrees of intensity, the latter 

 being somewhat confined to liquids, the former being equally 

 active in the air, we shall proceed to trace the consequence of 

 their action*. 



Before entering into the inquiry respecting the effects of the 

 positive and negative poles of the great terrestrial battery on the 

 surface of the earth, we shall first examine more in detail the 

 action of Electro-magnetism, by experiments. 



CHAPTER III. 



ON THE REDUCTION OF METALS BY ELECTRO-MAGNETISM 

 OR GALVANIC CURRENTS. 



When metals are observed in rocks or veins in their metallic 

 state, which is of common occurrence in metalliferous districts, 

 persons are too apt to think that such metals must have been 

 produced by some intense heat, similar to that applied in smelt- 

 ing works. Such an idea arises more from the habit of our 

 looking at metals as the production of our ordinary artificial 

 process of reducing minerals, than to any cause that can be as- 

 signed for this being the only mode of their formation. 



When we make a casting of any metal, even the most fusible, 

 we find a great difficulty in getting it to take the exact impres- 



* Ritter asserted that a needle, composed of silver and zinc, had arranged 

 itself in the magnetic meridian, i. e. the zinc towards the south and the silver 

 towards the north, and was slightly attracted and repelled by the poles of the 

 magnet : to effect this the air must be very moist. Generally speaking, such 

 needles can only act when immersed in liquid. In the air the needle must 

 be composed of such substances as will be capable of decomposing that element 

 to indicate polarity. It is a singular fact that those rocks which contain man- 

 ganese combined with iron ore are the most magnetic, and will preserve longer 

 their polarity. 



C 



