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.
423. The elements of the air, polarized to the highest degree by electricity, must combine, and this combination is the process of combustion. The final result of electrical tension is combustion of air. It is only, however, the two primary bodies that undergo combustion; the two constituent parts of the air must, therefore, be driven by electricity to their last extreme, even to the most perfect element of fire and the basic or terrestrial substance. The internal combination of both these primary or elemental bodies, or the product of this aerial combustion is next of all _water_. The termination of electrical tension in the air is rain. All rain is the extinguished function, the dying spirit of air. The two hostile principles are reconciled in water. Water accompanies every process of combustion.
424. By electricity the air was separated into the two inferior elements, into water and earth. At present, where the whole water and the whole earth has been precipitated from air, rain is certainly as a rule only water condensed and held in solution in the air.
425. The nitrogen gas is the residue of the primary rain. After the air has become sea by the combination of oxygen and hydrogen, it no longer creates water out of its own bulk, but now rederives it from the sea, and still but imitates its primary process in rain.