The chapter studies this mechanism in detail and focusses on the following questions. First, what are these ‘exhalations’ (ἀναθυμιάσεις) and why do they rise up in the sky? Secondly, why does the desiccation of the sublunary region cause celestial fire to descend to this region? More particularly, why does not celestial fire consume the sublunary region before it totally dries out, as an ordinary wildfire would consume a forest that is still relatively green and full of life? Thirdly, how does celestial fire consume the exhalations and the substances that it finds in the sublunary region? And, more generally, how do the Stoics conceive of the physical process by which a mass of fire consumes another body? In other words, how do they envision the phenomenon of combustion? Fourthly, what is the place of the concept of combustion in their elemental theory? And, finally, how long does the conflagration last?