n
that it must be attributed to the passage of light through icy
particles. Such, also, is the opinion of De Saussure, Scoresby, and
other meteorologists.

In regard to the mountains, as we cannot assure ourselves directly of
the fact by entering the clouds, we are reduced to conjecture. The
aerostat traversing the clouds completely, and passing by the very
point where the apparition is seen, affords one an opportunity of
ascertaining the state of the cloud. This observation I have been able
to make, and so to offer an explanation of the phenomenon.

As the balloon sails on, borne forward by the wind, its shadow travels
either on the ground or on the clouds. This shadow is, as a rule,
black, like all others; but it frequently happens that it appears
alone on the surface of the ground, and thus appears luminous.
Examining this shadow by the aid of a telescope, I have noticed that
it is often composed of a dark nucleus and a penumbra of the shape of
an aureola. This aureola, frequently very large in proportion to the
diameter of the central nucleus, eclipses it to the naked eye, so that
the whole shadow appears like a nebulous circle projected in yellow
upon the green ground of the woods and meadows. I have noticed, too,
that this luminous shadow is generally all the more strongly marked in
proportion to the greater humidity of the surface of the ground.

Seen upon the clouds, this shadow sometimes presents a curious aspect.
I have often, when the balloon emerged from the clouds into the clear
sky, suddenly perceived, at twenty or thirty yards' distance, a second
balloon distinctly delineated, and apparently of a grayish color,
against the white ground of the clouds. This phenomenon manifests
itself at the moment when the sun re-appears. The smallest details of
the car can be made out clearly, and our gestures are strikingly
reproduced by the shadow.

[Illustration: THE SHADOW OF THE BALLOON WAS SEEN BY US.]

On April 15, 1868, at about half-past three in the afternoon, we
emerged from a stratum of clouds, when the shadow of the balloon was
seen by us, surrounded by colored concentric circles, of which the car
formed the centre. It was very plainly visible upon a yellowish white
ground. A first circle of pale blue encompassed this ground and the
car in a kind of ring. Around this ring was a second of a deeper
yellow, then a grayish red zone, and lastly as the exterior
circumference, a fourth circle, violet in hue, a