s of space and time in a general and
comparative way. We can state the distances if we please in millions
of miles, or we can reckon the ampler spaces by using the interval
which separates the earth from the sun as we do a foot rule in our
ordinary work, but the depths of the starry spaces can only be sounded
by the winged imagination.

Although the student has been advised to begin his studies of Nature
on the field whereon he dwells, making that study the basis of his
most valuable communications with Nature, it is desirable that he
should at the same time gain some idea as to the range and scope of
our knowledge concerning the visible universe. As an aid toward this
end the following chapters of this book will give a very brief survey
of some of the most important truths concerning the heavens and the
earth which have rewarded the studies of scientific men. Of remoter
things, such as the bodies in the stellar spaces, the account will be
brief, for that which is known and important to the general student
can be briefly told. So, too, of the earlier ages of the earth's
history, although a vast deal is known, the greater part of the
knowledge is of interest and value mainly to geologists who cultivate
that field. That which is most striking and most important to the mass
of mankind is to be found in the existing state of our earth, the
conditions which make it a fit abode for our kind, and replete with
lessons which he may study with his own eyes without having to travel
the difficult paths of the higher sciences.

Although physiography necessarily takes some account of the things
which have been, even in the remote past, and this for the reason that
everything in this day of the world depends on the events of earlier
days, the accent of its teaching is on the immediate, visible, as we
may say, living world, which is a part of the life of all its
inhabitants.

CHAPTER III.

THE STELLAR REALM.

Even before men came to take any careful account of the Nature
immediately about them they began to conjecture and in a way to
inquire concerning the stars and the other heavenly bodies. It is
difficult for us to imagine how hard it was for students to gain any
adequate idea of what those lights in the sky really are. At first men
imagined the celestial bodies to be, as they seemed, small objects not
very far away. Among the Greeks the view grew up that the heavens