What is true for the particular substances which originally led man to discover the dual nature of electricity, holds good equally for any pair of substances capable of assuming the electric state when rubbed against each other. If we examine from this point of view the series of such substances, as usually given in the textbooks on electricity, we shall always find a substance of extreme salt-character at the one end, and one of extreme sulphur-character at the other, the substances as a whole forming a gradual transition from one extreme to the other. Which kind of electricity appears on each, when submitted to friction, depends on whether the counter-substance stands on its right or left, in the series. It is the particular relation between the two which makes them behave in one way or the other.

The similarity between this process and the frictional generation of electricity is evident.

Let us, to begin with, compare a mass of solid iron with the same quantity of it in powdered form. The difference is that the powder lacks the binding force which holds the solid piece together. Now lei us expose the powdered iron to the influence of a magnet. At once a certain ordering principle takes hold of the single particles. They no longer lie at random and unrelated, apart from the inconspicuous gravitational effect they exert on one another, but are drawn into a coherent whole, thus acquiring properties resembling those of an ordinary piece of solid matter.

It is known to-day that what nature reveals so strikingly in the case of the electric fish, is nothing but the manifestation of a principle at work in the bodies of all beings endowed with sensation and volition - in corporeal terms, with the duality of a nervous and a muscular system - and therefore at work also in the human body. Observation has shown that the activities of these two systems in man and animal are accompanied by the occurrence of different electric potentials in different parts of the body. Plate A, Fig. iii, shows the distribution of the two polar electric forces in the human body. The bent lines in the diagram stand for curves of equal electric potential. The straight line between them is the neutral zone. As might be expected, this line runs through the heart. What seems less obvious is its slanting position. Here the asymmetry, characteristic of the human body, comes to expression.

An example of this will appear in the next part of our studies, devoted to observations in the field of optics.

There are cases which seem to elude this law, and investigation has shown that other characteristics of the rubbed bodies, such as surface quality, can have a modifying influence. For lack of a guiding idea they are treated in the textbooks as 'irregularities'. Observation led by a true polarity concept shows that in these cases also the rule is not violated. In this respect, interesting information can be gained from the observations of J. W. Ritter (1776-1810), an ingenious Naturphilosoph from the circle round Goethe, but to whom, also, physical science is indebted for his discovery of the ultra-violet part of the spectrum and of galvanic polarization. Among his writings there is a treatise on electricity, giving many generally unknown instances of frictional electricity which are in good accord with our picture and well worth investigating. According to Ritter, even two crystalline substances of different hardness, such as Calcite and quartz, become electric when rubbed together, the softer playing the part of 'resin' and the harder that of 'glass'.

Our observations have shown that the emergence of the electric state, whether it be caused by friction or galvanically, depends on matter entering into a condition in which its cohesion is loosened - or, as we also put it, on its being turned into 'dust' - and this in such a way that the escaping levity remains dust-bound. This picture of electricity now enables us to give a realistic interpretation of certain phenomena which, in the interpretation which the physicist of the past was bound to give them, have contributed much to the tightening of the net of scientific illusion.

Read thus, the phenomenon tells us that a part of space occupied by a magnetic field has qualities which are otherwise found only where a coherent solid mass is present. A magnetic piece of solid iron, therefore, differs from a non-magnetic piece by giving rise in its surroundings to dynamic conditions which would otherwise exist only in its interior. This picture of the relatedness of magnetism to solidity is confirmed by the fact that both are cancelled by heat, and increased by cold.²

If we remember that the nervous system represents the salt-pole, and the metabolic system the sulphur-pole, of the human organism, and if we take into account the relationship between levity and gravity at the two poles, we can see from the distribution of the two electricities that the coupling of levity and gravity at the negative pole of the electrical polarity is such that levity descends into gravity, while at the positive pole gravity rises into levity. Negative electricity therefore must have somehow a 'spherical' character, and positive electricity a 'radial'.

When man in the state of world-onlooker undertook to form a dynamic picture of the nature of matter, it was inevitable that of all the qualities which belong to its existence he should be able to envisage only those pertaining to gravity and electricity. Because his consciousness, at this stage of its evolution, was closely bound up with the force of gravity inherent in the human body, he was unable to form any conception of levity as a force opposite to gravity. Yet, nature is built bipolarically, and polarity-concepts are therefore indispensable for developing a true understanding of her actions. This accounts for the fact that the unipolar concept of gravity had eventually to be supplemented by some kind of bipolar concept.