Fire and Earth Are the Causes of the Events in This World

We must treat fire and earth as the material causes of the events in this world. All its power and order is derived from them. The first difficulty is raised by what is called the air. What are we to take its nature to be in the world surrounding the earth, and what is its position relatively to the other physical elements? For there is no question as to the relation of the bulk of the earth to the size of the bodies which exist around it. We have already described and characterized the first element, and explained that the whole world of the upper motions is full of that body.