C. About the Place of Infernal Fire

48. On the second point [n.45]: Since fire only remains outside its sphere in continuous generation (according to the remark of the Philosopher, On Youth and Old Age [5.470a3-5], “it is always coming to be”), how would it persist in any complete sphere round the earth? How also would it purify things, since purification is only by the consuming of something impure, as of vapors or other such mixed bodies, in which there is impurity of air?