THE EARTH.

Its sign [Symbol].

DISTANCE FROM THE SUN, 92,500,000 MILES.  DIAMETER, POLAR, 7899 MILES; EQUATORIAL, 7925-1/2 MILES.  AXIAL REVOLUTION, 23H. 56M. 4.09S.; ORBITAL, 365.86.  ORBITAL VELOCITY PER MINUTE, 1152.8 MILES.

Let us lift ourselves up a thousand miles from the earth.  We see it as a ball hung upon nothing in empty space.  As the drop of falling water gathers itself [Page 142] into a sphere by its own inherent attraction, so the earth gathers itself into a ball.  Noticing closely, we see forms of continents outlined in bright relief, and oceanic forms in darker surfaces.  We see that its axis of revolution is nearly perpendicular to the line of light from the sun.  One-half is always dark.  The sunrise greets a new thousand miles every hour; the glories of [Page 143] the sunset follow over an equal space, 180 deg. behind.  We are glad that the darkness never overtakes the morning.

[Illustration:  Fig. 54.—­Earth and Moon in Space.]

The Aurora Borealis.

While east and west are gorgeous with sunrise and sunset, the north is often more glorious with its aurora borealis.  We remember that all worlds have weird and inexplicable appendages.  They are not limited to their solid surfaces or their circumambient air.  The sun has its fiery flames, corona, zodiacal light, and perhaps a finer kind of atmosphere than we know.  The earth is [Page 144] not without its inexplicable surroundings.  It has not only its gorgeous eastern sunrise, its glorious western sunset, high above its surface in the clouds, but it also has its more glorious northern dawn far above its clouds and air.  The realm of this royal splendor is as yet an unconquered world waiting for its Alexander.  There are certain observable facts, viz., it prevails mostly near the arctic circle rather than the pole; it takes on various forms—­cloud-like, arched, straight; it streams like banners, waves like curtains in the wind, is inconstant; is either the cause or result of electric disturbance; it is often from four hundred to six hundred miles above the earth, while our air cannot be over one hundred miles.  It almost seems like a revelation to human eyes of those vast, changeable, panoramic pictures by which the inhabitants of heaven are taught.

[Illustration:  Fig. 55.—­The Aurora as Waving Curtains.]

Investigation has discovered far more mysteries than it has explained.  It is possible that the same cause that produces sun-spots produces aurora in all space, visible in all worlds.  If so, we shall see more abundant auroras at the next maximum of sun-spot, between 1880-84.

The Delicate Balance of Forces.