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. Let us from this point of view contemplate the following series of chemical elements, which is a representation of the so-called voltaic series: Graphite, Platinum, Gold, Silver, Copper, Iron, Tin, Lead, Zinc, Aluminium, Magnesium, Sodium, Potassium. Any two of these metals constitute a voltaic cell. Its electromotive force is determined by the distance in the series between the metals used. Just as in the case of frictional electricity, the kind of electricity which is supplied by a certain metal depends on whether the other metal with which it is coupled stands to the right or to the left of it in the series.1