779. Terrestrial magnetism can only be based upon the polarity of metallic veins, and this upon the ores they contain. It must therefore accommodate itself to the distribution of the chief masses of metals, especially of the idiomagnetic metal. Now it has been ascertained, that the noble metals are accumulated about the equator, such as gold, silver, copper, which may be regarded as non-magnetic. In the northern temperate zones, the mountains contain for the most part metals that are non-magnetic and semi-noble, as lead, zinc, antimony, which are usually combined as ores with sulphur. Iron, on the contrary, being the only magnetic metal, (a fact which is also determined chiefly by the magnetic needle in terrestrial magnetism) is accumulated in greater quantity towards the north-pole and becomes always rarer in occurrence towards the equator. The southern hemisphere of the earth, is indeed less known in this respect; but, that towards the south-pole iron reincreases in quantity, is rendered evident by the magnetic needle when conveyed beyond the equator, inclining to the south-pole. If the cause of the inclination upon the northern hemisphere be sought for in the presence of iron, the same must be done in regard to the southern. The arrangement of the metallic groups from north-to south-pole is thus; iron, lead, silver, lead, iron. 780. Iron has been deposited at both poles and this in accordance with the genesis of metals, for iron is a half reduced metal, and must consequently be subjected to the demi-action only of light. At or beneath the equator the Ferrogeneous is wholly reduced, and becomes noble. 781. There is obviously, however, less iron at the south-than the north-pole, because the greatest part of the planet is there covered with water, and thus in general with less earth less metal also is to be found. From this alone it may be explained why the magnetic needle conveyed beyond the equator still remains horizontal and first inclines about the tenth degree of southern latitude towards the south-pole. 782. The north-pole is thus more energetic than the south-pole, so that the two poles must be also inversely related to each other. It is only from this antagonism of the two poles of the earth that we comprehend, why upon the southern hemisphere the south-pole of the needle dips towards the earth, and why the needle does not turn completely round. For if there was an equal quantity of iron in both hemispheres of the earth, the southern must have the same magnetic pole, and thus attract the north-pole of the needle; and under the equator the needle must have actually no direction. The cause of the direction and dip of the needle rests thus in the antagonism of the two poles of the earth, and this again in the unequal masses of iron.