The Philosophy of Roger Bacon

In the insubstantiality of its transparency, the upper part of the air does not differ from the lower part; therefore, in terms of sensible insubstantiality, it follows that vision from one to the other does not occur through refraction original: fractione; in medieval optics, refraction—the bending of light—was often called 'breaking.' because the air gradually increases in fineness. The heavens are equal to the lower part of fire in rarity and transparency, so that they are seen as one with the other. And yet, speaking consistently, there is a diversity of rarity there, because natural fire The "sphere of fire" was believed to be the highest and thinnest of the four elemental layers, located just below the moon. is rarer and more transparent; therefore, according to the rules and the base refers to the geometric "canons" or rules of the visual cone, where the base is the object seen, they are distinct things, or they might agree with one another and be equal in their harmfulness.

If indeed it is said that regarding these things, I prove it by the authors original: cathayorum, likely a scribal error for a known authority or "the books of the perspectives" in the Book of Aspects Alhazen’s De Aspectibus, the primary textbook for optics in the 13th century, as is clearly touched upon; they maintain that there is no dwelling-place for visible rays [within] the air by itself, just as for this reason it is not "toothed" original: dentata; perhaps meaning jagged or having a sharp boundary from the upper part of the air. From this, it seems to be of the same generation [nature], and thus they truly become one body. Because what is in the first principles and what is in the Meteorology Aristotle’s Meteorologia, which deals with the region between the earth and the moon is well-unified. And yet, by the nature of these things, they are divided. For Alhazen original: az; abbreviation for Alhazen (Ibn al-Haytham), the famous Arab polymath whose work Roger Bacon championed. says:

A dark stain and a physical hole in the parchment on the right side of the main text block obstruct parts of the text from line 14 to line 20. This damage obscures the technical explanation of how the air does not follow the nature of fire, though it mentions the "generation" of light and the quantities that exist between these spheres.

...and insofar as the air does not follow the nature of fire, which is of a visible kind and so is divided beneath the air, although it freezes... because there are divided quantities. If indeed it is said that it carries the transparent fineness in the manner of the heavens, it is said here at the beginning that this is not by divine nature but by their own reason, nor are they distinct in their base. Because regarding one another, it is not a matter of quantity but of quality; and so, in a universal sense, unity is not concluded, because by the reason of these things, they are nevertheless subtle in terms of the subtlety of their quality.

If, however, it is objected through Alhazen in the first book of the Meteorology, that air is confounded by fire, nevertheless in every triangle of them, it will be one. For in their divided kinds, parts of fire and parts of air are mentioned; but a successful penetration original: penetracio cannot happen through the whole kind as it does in the heavens, but is only partial. For a "meteor" In the 13th century, a "meteor" referred to any atmospheric phenomenon like a comet or lightning. penetrates the air and burns it; the air penetrates the fire, and this penetration is nevertheless visible. One kind nevertheless exists deep within the reason of the other, because here the air is drawn to the fire, and they pass through by reason of the insubstantiality of their fineness; thus the air is much ignited, and the fire is nevertheless air through itself, and through this accident, there is never [separation], and here the confusion of air and ignited fire is noted.

Furthermore, here Alhazen says that quantities are divided in three ways; nevertheless, it now approaches a different perfection through this similarity, namely, it is not a case of new generation but a certain contiguous passage which continues them. And therefore, there will be a twofold cause here; it is said among the "meteors" that the distinction of things seen ought to be contrary, as all men confess.

— Here there is a confusion. If it is said that all elements are in a state of refraction, so that all things are made; nevertheless, they have one through the other, as is taught by Alhazen.