Elements of Physiophilosophy

by Lorenz Oken

778. Thus the direction of the magnetic axis of the earth, its mutability, the declination of the magnetic meridian, the inclination or dip of the needle, in short every phenomenon without distinction that concerns magnetism, must be derived from the nature of the metallic veins. Another momentum does not indeed exist for magnetism.

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.

783. The action of terrestrial magnetism does not reside in the iron formation alone, but in its antagonism to the reduced ores. The terrestrial magnetism is a tension between iron and silver. The lead imparts the poles.

784. As the earth is a globe, so are the two masses of iron situated nearer to its axis than the masses of silver and lead. If therefore the latter exert also any influence upon the direction of the magnetic needle, yet nevertheless the poles of magnetism must coincide nearly with the poles of the earth's axis, because the exciters of magnetism operate in this direction.

785. The magnetic meridian runs indeed in general from pole to pole, but as it is not the earth's axis, which determines the magnetism, but the metallic masses, so the direction of the meridian deviates from the earth's axis in accordance with these masses.

786. The magnetic needle can therefore assume a different direction on every part of the earth, according as its relative position is varied between two principal masses of metals, and even as is indicated by the movement of the compass with the change of geographical longitudes, it is removed from one metallic mass, approaches another, and by this becomes more powerfully attracted. Upon the whole, however, the direction must tend toward the poles. Such are the phenomena of declination of the magnetic needle; and we can now comprehend why this is present.

787. But there must be also spots upon the earth, where the needle points straight to the north, probably, when it is between two metallic masses, or stands at a certain angle to them. These are the lines without declination, of which there are many as is well known, but which have not as yet been reduced to any law. Nor can they ever be so, because we shall never become acquainted with the metallic beds.