418. The + E is the more energetic, active in itself, polar; it is the electricity of fire represented in oxygen. The-E is the weaker, that which has only been evoked, the basic; it is the electricity of the planet represented in nitrogen, hydrogen, carbon, sulphur. It may be said that-E is related to + E as planet is to sun, as periphery to centre. The sun is + E, the planet-E, the one the electricity of oxygen, the other of hydrogen. 419. These electrical conditions must always be changing in the air, according as the slightest influence is brought to bear upon them from without. The air consists in this change of electrical poles. Were the poles not to change, the air would be a solid element. The earth is an air with _fixed_ electricity, the water with extinguished or neutralized electricity. 420. The twofold character of the aerial principles is increased by every polarizing action from without, and therefore principally by the surface of the earth, which consists of two elements. Were there no surface to the earth, were simply air present, then there would be no electrical change of poles. The surface of the earth itself, however, produces no change of poles in the air, for it remains always neutral; but it becomes unequal or polar from the change wrought upon it by water and earth, by light, by heating and by chemical processes. 421. The air also changes the electricities while it roams over the earth. This wandering motion is a contact of differently polarized tracts of the earth. Every mountain, valley, and river, every meadow is differently polarized; from each the air derives another electricity. Through this ceaseless alternation of polar exchange, its activity becomes so elevated that at last the electricity makes its appearance in a manner cognizable by the senses. The production of electricity by _friction_ admits of a similar explanation. Friction is in miniature, what the sweeping of air is over the earth. Were the earth quite level, and composed of homogeneous matter, the air would not become electric by motion. 422. All terrestrial electricity has been evoked by a change of poles analogous to friction. Through light nothing foreign is posited in the air, any more than by friction, and by both the electricity is attained in a similar dynamical manner.