Wonders of Earth, Sea and Sky | Page 3

has still to grow almost infinitely before
anything like a complete explanation even of external Nature is
achieved.
Suppose that, at some future day, all physical and mechanical laws
should be found to be direct consequences of a single majestic law, just
as all the motions of the planets are (but--are they?) the direct results of
the single law of gravitation. Gravitation will, probably, soon be
explained in terms of some remoter cause, but the reason of that single

and ultimate law of the universe which we have imagined would still
remain unknown. Human knowledge will always have limits, and
beyond those limits there will always be room for mystery and wonder.
A complete and exhaustive explanation of the world is inconceivable,
so long as human powers and capacities remain at all as they now are.
It is important to emphasize such truths, especially in a book addressed
to the young. When a lad hears for the first time that an astronomer, by
a simple pointing of his spectroscope, can determine with what velocity
a star is approaching the earth, or receding from it, or when he hears
that the very shape of the revolving masses of certain stars can be
calculated from simple measures of the sort, he is apt to conclude that
Science, which has made such astounding advances since the days of
Galileo and Newton, must eventually reach a complete explanation of
the entire universe. The conclusion is not unnatural, but it is not correct.
There are limits beyond which Science, in this sense, cannot go. Its
scope is limited. Beyond its limits there are problems that it cannot
solve, mysteries that it cannot explain.
At the present moment, for example, the nature of Force is unknown. A
weight released from the hand drops to the earth. Exactly what is the
nature of the force with which the earth attracts it? We do not know,
but it so happens that it is more than likely that an explanation will be
reached in our own day. Gravity will be explained in terms of some
more general forces. The mystery will be pushed back another step, and
yet another and another. But the progress is not indefinite. If all the
mechanical actions of the entire universe were to be formulated as the
results of a single law or cause, the cause of that cause would be still to
seek, as has been said.
We have every right to exult in the amazing achievements of Science;
but we have not understood them until we realize that the universe of
Science has strict limits, within which all its conquests must necessarily
be confined. Humility, and not pride, is the final lesson of scientific
work and study.
* * * * *
The choice of the selections printed in this volume has been necessarily
limited by many hampering conditions, that of mere space being one of
the most harassing. Each of the chapters might readily be expanded into
a volume. Volumes might be added on topics almost untouched here. It

has been necessary to pass over almost without notice matters of
surpassing interest and importance: Electricity and its wonderful and
new applications; the new Biology, with its views upon such
fundamental questions as the origins of life and death; modern
Astronomy, with its far-reaching pronouncements upon the fate of
universes. All these can only be touched lightly, if at all. It is the chief
purpose of this volume to point the way towards the most modern and
the greatest conclusions of Science, and to lay foundations upon which
the reading of a life-time can be laid.
[Illustration: Signature: Edward S. Holden]
UNITED STATES MILITARY ACADEMY, WEST POINT, _January
1, 1902_.

WONDERS OF EARTH, SEA, AND SKY

WHAT THE EARTH'S CRUST IS MADE OF
(FROM THE WORLD'S FOUNDATIONS.)
BY AGNES GIBERNE.
"Stand still and consider the wondrous works of God."
[Illustration]
What is the earth made of--this round earth upon which we human
beings live and move?
A question more easily asked than answered, as regards a very large
portion of it. For the earth is a huge ball nearly eight thousand miles in
diameter, and we who dwell on the outside have no means of getting
down more than a very little way below the surface. So it is quite
impossible for us to speak positively as to the inside of the earth, and
what it is made of. Some people believe the earth's inside to be hard
and solid, while others believe it to be one enormous lake or furnace of
fiery melted rock. But nobody really knows.
This outside crust has been reckoned to be of many different
thicknesses. One man will say it is ten miles thick, and another will rate
it at four hundred miles. So far as