abalistic
philosophers, who fancy spirits in every element, calling those sylphs
which they pretend to inhabit the air; _gnomes_, those which they
feign to be under the earth; _ondines_, those which dwell in the
water; and _salamanders_, those of fire; we acknowledge but three
sorts of created spirits, namely, angels, demons, and the souls which
God has united to our bodies, and which are separated from them by
death.

"The Holy Scriptures speak in too many places of the apparitions of
the angels to Abraham, Jacob, Tobit, and several other holy patriarchs
and prophets, for us to doubt of it. Besides, as their name signifies
their ministry, being created by God to be his messengers, and to
execute his commands, it is easy to believe that they have often
appeared visibly to men, to announce to them the will of the Almighty.
Almost all the theologians agree that the angels appear in the aerial
bodies with which they clothe themselves.

"To make you understand in what manner they take and invest themselves
with these bodies, in order to render themselves visible to men, and
to make themselves heard by them, we must first of all explain what is
vision, which is only the bringing of the _species_ within the compass
of the organ of sight. This "_species_" is the ray of light broken and
modified upon a body, on which, forming different angles, this light
is converted into colors. For an angle of a certain kind makes red,
another green, blue or yellow, and so on of all the colors, as we
perceive in the prism, on which the reflected rays of the sun forms
the different colors of the rainbow; the _species_ visible is then
nothing else than the ray of light which returns from the object on
which it breaks to the eyes.

"Now, light falls only on three kinds of objects or bodies, of which
some are diaphanous, others opake, and the others participate in these
two qualities, being partly diaphanous and partly opake. When the
light falls on a diaphanous body which is full of an infinity of
little pores, as the air, it passes through without causing any
reflection. When the light falls on a body entirely opake, as a
flower, for instance, not being able to penetrate it, its ray is
reflected from it, and returns from the flower to the eye, to which it
carries the _species_, and renders the colors distinguishable,
according to the angles formed by reflection. If the body on which the
light falls is in part opake and in part diaphanous, l