The phenomenon actually takes place in this manner in the parts of the
atmosphere that are the most distant from the earth. We perceive what
are termed auroral plates of a purple or reddish-violet color, more or
less extended, according as this species of veil, formed by icy
particles, extends to a greater or less distance from the poles. The
tenuity of this veil is such that it admits of our seeing the stars
through the auroral plates. Of its existence, independently of indirect
proofs, we have a direct demonstration in the observation of MM. Bixio
and Baral, who, being raised in a balloon to a great height, found
themselves, on a sudden, although the sky was entirely serene and the
atmosphere cloudless, in the midst of a perfectly transparent veil,
formed by a multitude of little icy needles, so fine that they were
scarcely visible.
If we place the pole of an electro-magnet over the jets of electric
light that are made to converge in extremely rarefied air, we shall see
that the electric light, instead of coming out indifferently from all
points of the upper surface, as had taken place before the
magnetization, comes out from the points of the circumference only of
this surface, so as to form around it a continuous luminous ring.
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