Some writers are firmly convinced that the lightning bolt always 1 returns to the clouds. Others hold that the bolt settles in the ground, at least when its fuel is heavy, and when it has comparatively little force in its stroke as it glides down. But why, it may be asked, does the bolt make its appearance suddenly, and is there not a continuous trail of fire? It is on account of the extreme rapidity of its motion; it fires the air at the same moment as it bursts through the cloud. By and by when the motion ceases, the flame subsides. For the course of the air that forms the bolt is intermittent, which 2 prevents continuity in the fire. As often as the air by its more violent agitation sets itself on fire it conceives an impulse toward flight. When the internal conflict has been ended by its escape, it is afterwards for the same reason sometimes carried down as far as the earth, and sometimes, if urged down with less force, it is dissipated in air. Why, again, is the course of the lightning oblique? The reason is that the air current of which it is composed is oblique and tortuous. Nature summons fire upward, violence presses it downward, 3 and so it begins to be zigzag. Sometimes, when neither force gives way to the other, the fire is at the same moment urged toward the upper and depressed toward the nether regions. Why are the peaks of mountains frequently struck by it? Because they are exposed to the clouds, and objects falling from heaven to earth must pass by way of them. LIX