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This matter is well known to those who are
astronomers. It is it that now gives us the blue
color that extends above into the are, which
we see when the air is pure and clean all around. And
it is so well balanced (of such great equilibrium) that there
may be no violence there. This is the sky that encloses the
firmament. But I tell you very openly that that you may
can understand by hearing of it, that no one can take
anything nor benefit, nor prove it is the truth or not by
any art of demonstration the way one can see with one's eyes.
For man has no sense that is capable of it. But even so I
tell you that we can find the truth by that which is written:
in certain places. For some ancient philosophers were
thinking of it, for which they found certain reasons.
[rubric:] This speaks of the crystalline sky and the empyrean sky. [/rubric]
Above the sky that we can see, as it is
said according to them [the] ancient philosphers,
there is another sky that is all around it, above and
beneath, and that one is like the color of crystal,
white and clear and very pure, and clear and noble,
and it is called the crystalling sky. And above this crystalline sky all