equilibrium between the positive electricity of the vapors and the
negative electricity of the earth must be accomplished by means of a
discharge, which, when of sufficient intensity, will be accompanied
with light, if, as is almost always the case near the poles, and
sometimes in the higher parts of the atmosphere, it take place among
those extremely small icy particles which constitute the hazes and the
very elevated clouds.

There can be no doubt that the occurrence of the phenomenon is
materially dependent on the presence in the atmosphere of these
particles of ice, forming a kind of thin haze, which, becoming luminous
by the transmission of electricity, must appear simply as an
illuminated surface of greater or less extent, and more or less cut up.
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