Prelude

...[by all these] factors, driven both by Princes of the highest authority and by my own curiosity for investigating the secrets of nature, it seemed fit to compose this present little work. In it, I retain the substance of everything explained by the Holy Fathers and established by modern observations; however, I proceed with a different method, resolving each point to its ultimate principles in a way that, as far as I know, perhaps no one has done before me. I have done this to such an extent that whatever I have brought forward in this entire little work regarding the wonders of marvelous phenomena Original Greek: φαινομένων (phainomenon), meaning "appearances" or things observed in the sky. may be called not so much inventions fashioned by my own wit, but rather certain logical consequences resulting from the stated authorities and observations.

I have used this reasoning: if the heaven, or firmament, is liquid In this context, "liquid" (liquidum) means fluid or flowing, like air or water, rather than a solid crystalline sphere as older medieval science suggested., as the Holy Fathers explain from Sacred Scripture, then the heaven must be one and threefold, everywhere passable and everywhere penetrable, placing no obstacles or barriers to the astral bodies The stars and planets. moving within it. It is one in its continuous fluidity, yet threefold in the distinction of its regions; these are the aerial, the starry, and the empyrean heaven. It is to this last one that they say Saint Paul was caught up; yet, just as it is far removed beyond all limits of the natural order, it is reached by faith alone.

St. Augustine

Moreover, Saint Augustine explains that the liquid firmament is composed of fire and water in Book 3 of The Literal Meaning of Genesis, chapter 6, using these words:

The firmament in which the luminaries are is contained partly by the upper air and partly by the ethereal fire;

He explains this more at length in chapters 7, 9, and 10, where he does nothing else than provide a rigorous [explanation] to those consulting him about these sayings...