ced the countless
_atolls_ of the Pacific, and by the vast upheavals of thousands of miles
of heated rocks of the primary formations into the beds of primeval
oceans. While such processes were in progress, it was impossible but
that darkness should be upon the face of the deep.[267] Even now, a
slight change of atmospheric density and temperature would vail the
earth with darkness. We see this substantially done every time that God
"covereth the light with clouds, and commandeth it not to shine by the
cloud that cometh betwixt," although the sun continues to shine with all
his usual splendor. To understand how there may be a day without
sunshine, we need only conceive the whole earth temporarily enveloped
in the vapors of the unastronomical atmosphere of Peru, thus described
by Humboldt:

"A thick mist obscures the firmament in this region for many months,
during the period called _tiempo de la garua_. Not a planet--not the
most brilliant stars of the southern hemisphere--are visible. It is
frequently almost impossible to distinguish the position of the moon.
If, by chance, the outline of the sun's disc be visible during the day,
it appears devoid of rays, as if seen through colored glasses. According
to what modern geology has taught us to conjecture concerning the
ancient history of our atmosphere, its primitive condition in respect to
its mixture and density _must have been unfavorable to the transmission
of light_. When we consider the numerous processes which, in the primary
world, may have led to the separation of the solids, fluids, and gases
around the earth's surface, the thought involuntarily arises, _how
narrowly the human race escaped being surrounded with an untransparent
atmosphere_, which, though not greatly prejudicial to some classes of
vegetation, would yet have completely vailed the whole of the starry
canopy. All knowledge of the structure of the universe could then have
been withheld from the inquiring spirit of man."[268] The sun, then, may
have shone with all his brilliancy, for thousands of years, and a single
ray never have penetrated the darkness upon the face of the deep.

But we will go further, and show that so far from light being an
essential property of suns, it is a very variable attribute, and that in
several cases suns have ceased, and others begun, to shine, before our
eyes.

The fixed stars are self-luminous bodies, similar to our sun, only
immensely distant from us. Their numbers