e greeted, and studied, as
the index of the operation of very positive cosmical functions.

HUMBOLDT regarded this process as "the restoration of a disturbed
equilibrium;" and so indeed it is, but it is an equilibrium, not simply
as between the earth, and atmosphere. Various observers have estimated
the altitude to which the aurora sometimes reaches, at from 80 to 265
miles. The fact that the _bulk_ of the atmosphere reaches but _three
miles_ above the earth's surface, forbids it to be regarded as purely a
terrestro-atmospheric phenomenon.

While viewing the more striking and brilliant exhibitions of the aurora,
the more undemonstrative and by far the most important and vital
operations have been disregarded. The former may not be observed, except
occasionally, and fitfully, _can_ only be present when favoring
meteorological conditions admit of its disclosure. The latter, more
unobtrusive and even invisible to the naked eye, are incessantly, and at
all seasons, in action, by day as well as by night.[9] May not this
auroral display then be regarded in a measure as confirmatory of what
the law of conservation had already suggested to us; the existence of a
_retro_-current?

_Well understood Processes in Confirmation._

The suggestion of a simple, adequate, and perfect theory is given us by
an ordinary electro-magnetic battery. Let the conducting wire from such
a battery extend half around the circumference of this globe. It is
apparently as quiet and dormant as is our earth; yet in those cold
plates, solutions, and wire, there lie the hidden elements of heat,
light, and power. At the distant extremity of the wire, when not
connected with the earth, we may have none of the manifestations of
heat, light, or attraction--even though the plates are put into the
solution. But let us now make the connection between the extremity of
the wire and the earth, _then_ the circuit is complete, and heat, light,
and attraction are disclosed in highest degree.

Now from the _Great Sun Battery_,[10] in which we locate the one _Great
Universal Force: Newton's "Higher and Still Unknown Force,"_ every
one recognizes a current constantly present, setting towards the earth.
That current is recognized as bringing us our light and heat. But
without a _retro_-current, should we have a circuit complete? Should we
have any of these phenomena?

_Heat without Combustion._

Neither _in_ the battery nor _ne