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 regards man’s knowledge of it, gained from mining, from boring, from examination of rocks, and from reasoning out all that may be learned from these observations, we shall allow an ample margin if we count the field of geology to extend some twenty miles downwards from the highest mountain-tops.  Beyond this we find ourselves in a land of darkness and conjecture.