ike glass, it
passes through the diaphanous part, that is to say, through the pores
of the glass which it penetrates, and reflects itself on the opake
particles, that is to say, which are not porous. Thus the air is
invisible, because it is absolutely penetrated with light: the flower
sends back a color to the eye, because, being impenetrable to the
light, it obliges it to reflect itself; and the glass is visible only
because it contains some opake particles, which, according to the
diversity of angles formed upon it by the ray of light, reflect
different colors.

"That is the manner in which vision is formed, so that air being
invisible, on account of its extreme transparency, an angel could not
clothe himself with it and render himself visible, but by thickening
the air so much, that from diaphanous it became opake, and capable of
reflecting the ray of light to the eye of him who perceived him. Now,
as the angels possess knowledge and power far beyond anything we can
imagine, we need not be astonished if they can form aerial bodies,
which are rendered visible by the opacity they impart to them. In
respect to the organs necessary to these aerial bodies, to form sounds
and make themselves heard, without having any recourse to the
disposition of matter, we must attribute them entirely to a miracle.

"It is thus that angels have appeared to the holy patriarchs. It is
thus that the glorious souls that participate the angelic nature can
assume an aerial body to render themselves visible, and that even
demons, by thickening and condensing the air, can make to themselves a
body of it, so as to become visible to men, by the particular
permission of God, to accomplish the secrets of his providence, as
they are said to have appeared to St. Anthony the Hermit, and to other
saints, in order to tempt them.

"Excuse, sir, this little physical digression, with which I could not
dispense, in order to make you understand the manner in which angels,
who are purely spiritual substances, can be perceived by our fleshly
senses.

"The only point on which the holy doctors do not agree on this subject
is, to know if angels appear to men of their own accord, or whether
they can do it only by an express command from God. It seems to me
that nothing can better contribute to the decision of this difficulty,
than to determine the way in which the angels know all things here
below; for if it is by means of "_species_" which God communicates to