XXII
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Now that it is agreed that the two things are both fire, let us see how fire arises on earth, for no doubt the same method prevails aloft. There are two common methods of producing fire—one by striking it out, as, for example, from a stone; the other by the more tedious method of friction, as when two pieces of wood are rubbed together for some time. It is, of course, not every kind of substance that gives the desired result; you must choose one suitable for giving out fire, for example, laurel, ivy, and other trees familiar to shepherds for this purpose. Probably, therefore, clouds may in the same way emit fire either from a blow or from friction. Consider for a moment the force with which squalls rush forth, the impetuous eddying revolution of the whirlwind. Anything that encounters a missile from an engine of war is scattered and removed and driven far from its position. What wonder, then, that such violence in the wind extracts fire either from some external object or merely from itself? You can readily see what a glow all neighbouring bodies grazed by its passage must receive. But the force of storms cannot for a moment be compared with the energy of the heavenly bodies, whose immense power is beyond question.