an 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-