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OBSERVATIONS ON THE AURORA BOREALIS.

vertical angle, formed by the visual ray from the body and the plane of the horizon ;it is therefore the elongation of a streamer towards the zenith of the observer thatcauses the appearance of ascent or shooting upwards, and no real increase of distancefrom the earth’s surface. When streamers pass the zenith, their increase in lengthgives them the appearance of a dowmvard motion, which is also the case, whatever maybe their course, provided the progress of elongation is from the spectator.

From the observed influence of electrical forces in giving forms to, and producingintestine commotions in, thunder-clouds, there is reason to infer that similar forcesare productive of peculiar forms and arrangements of aqueous vapour in regions muchhigher than those groups of heavy clouds ; and that electrical transmissions may beaccomplished through conductors which had been formed by electrical forces, but nosuch formations of conducting material could take place exterior to the atmosphere,where none is in existence.

It is a well-ascertained fact that the electric fluid is more abundant in the upperparts of the atmosphere than in the inferior strata ; and that this is the normal stateof the air when undisturbed by clouds or other causes. Hence, were this normal stateto remain unruffled, there would be a steady equilibrium of electric forces throughoutthe atmosphere, and an electrical tranquillity would be permanently established inevery part of it. Such a tranquillity, however, cannot possibly exist in an atmospherethat is subject to continual fluctuations of temperature, moisture, and consequentwinds ; hence the natural tendency to an electrical equilibrium is ever being inter-rupted, and electrical commotions of more or less magnitude are continually going on.

When the air is highly charged with aqueous vapour, and suffers a sudden depres-sion of temperature, dense clouds are formed with amazing rapidity, and the electricfluid being condensed in them to a higher degree of intensity than they can retain it,liberates itself from this aqueous imprisonment in the shape of lightning. In the upperregions of the air, where the insulation is much less perfect, no lightning cloud canpossibly be formed ; because the electric fluid, finding but little resistance to its move-ments, however suddenly it may be disturbed by change of temperature, flows fromone part to another before its intensity gets sufficiently high to form lightning or dis-charge itself in a close compact body; hence, any sudden disturbance of the electricfluid in the upper regions of the atmosphere, instead of producing lightning, wouldcause it to move in waves, or as a diffused ocean, in those directions offering the leastresistance, covering an extensive area in its transit. Such an electric tide occurringat night-time would be visible, and partake of all the forms of the conducting mediathrough which it passed.

Now, it being a well-established fact that attenuated air is a better conductor thanair of greater density, and that a vacuum is a better conductor than attenuated air—and, as the attenuated regions of the atmosphere are more highly charged with the