the world in a second of our clock-time, which
takes eight minutes and seventeen seconds to
reach us from the sun, which is travelling two-
and-twenty long years before it arrives here from
the dog-star—is estimated to require not less
than a million of years to traverse the enormous
space which lies between us and the furthest
stars of the furthest perceptible nebulæ.

The physical difference between stars and
planets is not so great as it appears, being
probably a question of time merely, of cooling
down. Unless geologists are greatly mistaken,
Descartes' description of the Earth as "a sun
covered with a crust," is correct. The Earth is
a spherical egg-shell filled with fiery contents.
The sun himself may possibly be one day
covered with a crust, if we could peel the
Earth as we peel an apple, with about the same
proportional thickness of paring, the Earth
would become a little sun. Bottom-heat, so
beloved of modern gardeners, was not wanting
to the primitive vegetation which comes down
to us in the shape of coal. Our actual continents
repose and float upon the internal nucleus
of the Earth, which is still in a state of fusion,
or even of fluid elasticity. Whithersoever we
direct our steps, we walk upon very tender
ground. Earthquakes, upraisings and depressions
of the soil, are only slight and gentle
approaches to an ulterior equilibrium between
the thin outside crust and the bulky mass of
fluid within, which is compressed with a force
equal to the weight of fourteen hundred atmospheres.
Round and above the elastic fluid
mass, lies, we are told, a stratum of lava, which
in turn is covered by a solid crust of earth not
more than forty miles in thickness. Some
authorities reduce that depth by one-half. In
consequence of greater cooling, the Earth's
crust is thicker at the poles than at the equator;
which does not prevent Hecla and Geysers from
making their pyrotechnic and hydraulic displays.
It will be evident that earthquakes
are the natural result of a pliable flooring
resting on a liquid mass; exactly as the ice-
fields of the polar seas are rent by the heaving
of the waters beneath them. In this world
there is no absolutely stable foundation. The
Edinburgh Observatory has verified the permanent
oscillation of the ground—a fact which
has likewise been manifested in other observatories,
to the great annoyance of astronomers,
who are thus placed, to a certain degree, in the
uncomfortable position of observers on ship-
board.

When the terrestrial crust cracks, in consequence
of any change of form, the lava is forced
through the fissure and there makes its escape.
Sometimes even the internal gas boils up and
pierces through the lava, projecting, to an altitude
of thirty thousand feet and more, a substance
analogous to glass which has not only
been melted but reduced to the state of vapour.
These vapours fall in the shape of ashes, or
rather of volcanic sand, whose nature is so clear
and decided, that, amongst other volcanic
products, natural glass has been found capable of
being made into bottles, razors, and other
utensils.

In general, the cracks in the Earth's crust
run on and are continued in the same direction.
In France, the whole line of the Rhine presents
an almost uninterrupted succession of cracks
and inactive volcanoes. In Auvergne, similar
quiescent volcanoes lie all in a complete and
perfect row. In America, the whole mountain
chain which skirts the Pacific betrays the existence
of numerous clefts and fissures. But the
internal convulsions of the globe do not always
break out at the surface. In 1760, subterranean
noises, like the rolling of thunder, were heard at
Honfleur, in Normandy, without producing any
further disturbance.

Hot springs are a natural result of the Earth's
internal heat. Every spring which drains into a
cavity of considerable depth, will find its walls
of rock hot enough to make it boil, and will
issue in the state of thermal water. If it be also
charged with foreign matters, it becomes not
only a thermal but a mineral spring. From a
depth of more than seventeen hundred feet, the
artesian well of Grenelle has supplied water at
eighty-two degrees of Fahrenheit.

At a sufficient depth the temperature would
be so high as to prevent water from penetrating
deeper. It would be instantly converted into
steam, and so sent back to the upper strata.
This is probably one of the causes which hinder
the infiltration and disappearance of the mass of
waters which cover the globe. The ocean is
water which cannot strain through a cullender,
by reason of the fierceness of the fire beneath it.
A red-hot sponge would not soak up water,
neither can red-hot caverns absorb the seas.

The long continuance of volcanoes and thermal
springs is a further proof of their deep-seated
origin. Mountains which, like Ætna and Vesuvius,
have been burning more or less throughout the
whole historic period; springs which were known
to be hot, and were visited for their healing
virtues, thousands of years ago; cannot have a
shallow source of heat. Happily, Earth, Water,
and Air, are all three bad conductors of heat.
Our central calorifere or warming-pan, which it
might be death to us to lose, has its heat retained
by the triple non-conducting wrapper formed by
the terrestrial crust, the ocean, and the cloudy
sky.

The central fire does more than warm us.
Heat, electricity, magnetism, are only correlative
forces. Lightning has been known to flash out
of the craters of burning mountains. The Earth,
say German dreamers, is a big animal, with a
loadstone inside it instead of a heart; and it
carries on its surface an ambiguous creature, the
Sea, electrical and phosphorescent, more sensitive
than itself, and infinitely more fecund. But
the Sea is no parasite of the great animal. It has
no distinct or hostile individuality. On the
contrary, it vivifies and fecundates the Earth
with its life-giving vapours. All which is merely
a figurative way of stating that all things
harmonise.

The Earth's place in the solar system is a