Clearly, then, in the case of electrical polarity we encounter a certain form of gravity-bound levity, and this in a twofold way. Owing to the contrasting nature of the two bodies involved in the process, the coupling of gravity and levity is a polar one on both sides. The electrical polarity thus turns out to be itself of the nature of a secondary polarity.
Two more recently discovered means of evoking the electric condition in a piece of matter confirm this picture. They are the so-called piezo-electricity and pyro-electricity. Both signify the occurrence of the electrical polarity at the two ends of an asymmetrically built (hemimorphous) crystal, as the result of changing the crystal's spatial condition. In piezo-electricity the change consists in a diminution of the crystal's volume through pressure; in pyro-electricity, in an increase of the crystal volume by raising its temperature. The asymmetry of the crystal, due to a one-sided working of the forces of crystallization, plays the same role here as does the alchemic opposition between the two bodies used for the production of frictional electricity.
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It is typical of the scientist of the past that he was dependent on phenomena brought about by a highly developed experimental technique for becoming aware of certain properties of the electrical force, whereas for the realistic observer these properties are revealed at once by the most primitive electric phenomena. We remember Eddington's description of the positron as 'negative material', and his subsequent remarks, which show the paradoxical nature of this concept if applied to the hypothetical interior of the atom (Chapter IV). The quite primitive phenomenon of electrical repulsion and attraction shows us the same thing in a manner of which it is not difficult to form a conception.
Modern physics itself, with the help of Faraday's field-concept, describes these phenomena as caused by pressure - resulting from the meeting in space of two similar electrical fields - and suction - resulting from the meeting of two dissimilar fields. In the first case the space between the two electrically charged bodies assumes a degree of density, as if it were filled with some elastic material. In the second instance the density of the space where the two fields intermingle is lower than that of its surroundings. Here, clearly, we have a state of negative density which acts on the electrically charged bodies just as a lowering of pressure acts on a gas: in both cases movement occurs in the direction leading from the higher to the lower density. Electricity thus shows itself capable of producing both gravity and levity effects, thereby once more confirming our picture of it.
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Our next task will be to examine the galvanic form of generating electricity, in order to gain further light on our picture of the electrical polarity.
Galvanism, as it became established through Volta's work, rests on certain properties of the metallic substances of the earth. Compared with the substances which may be used for producing electricity through friction, the metals hold a mid-position. They are all essentially mercurial substances. (In quicksilver, which for this reason was given the name 'mercury' by the alchemists, this fact comes to an ur-phenomenal appearance.) Among the many facts proving the mercurial nature of the metals, there is one of particular interest to us. This is their peculiar relationship to the processes of oxidation and reduction.
Metals, in their metallic state, are bearers of latent levity, which can be set free either through combustion or through corrosion. They differ from one another by their relative degree of eagerness to enter into and remain in the metallic, that is, the reduced state, or to assume and keep the state of the oxide (in which form they are found in the various metallic oxides and salts). There are metals such as gold, silver, etc., for which the reduced state is more or less natural; others, such as potassium, sodium, etc., find the oxidized state natural and can be brought into and kept in the reduced state only by artificial means. Between these extremes there are all possible degrees of transition, some metals more nearly resembling the 'noble', others more nearly the 'corrosive', metals.
We remember that it was the different relationship of sulphur and phosphorus to reduction and oxidation which led us to envisage them as ur-phenomenal representatives of the alchemic polarity. We may therefore say that there are metals which from the alchemic point of view more nearly resemble sulphur, others more nearly phosphorus, whilst others again hold an intermediary position between the extremes. It is on these differences among the various metals that their galvanic properties are based.