e facts, in order to see if they
accord with the assumed rule or law, which has given modern science
the sound footing that it lacked in earlier days, and which has
permitted our learning to go on step by step in a safe way up the
heights to which it has climbed. All explanations of Nature begin with
the work of the imagination. In common phrase, they all are guesses
which have at first but little value, and only attain importance in
proportion as they are verified by long-continued criticism, which has
for its object to see whether the facts accord with the theory. It is
in this effort to secure proof that modern science has gathered the
enormous store of well-ascertained facts which constitutes its true
wealth, and which distinguishes it from the earlier imaginative and to
a great extent unproved views.

In the original state of learning, natural science was confounded with
political and social tradition, with the precepts of duty which
constitute the law of the people, as well as with their religion, the
whole being in the possession of the priests or wise men. So long as
natural action was supposed to be in the immediate control of numerous
gods and demigods, so long, in a word, as the explanation of Nature
was what we term polytheistic, this association of science with other
forms of learning was not only natural but inevitable. Gradually,
however, as the conception of natural law replaced the earlier idea as
to the intervention of a spirit, science departed from other forms of
lore and came to possess a field to itself. At first it was one body
of learning. The naturalists of Aristotle's time, and from his day
down to near our own, generally concerned themselves with the whole
field of Nature. For a time it was possible for any one able and
laborious man to know all which had been ascertained concerning
astronomy, chemistry, geology, as well as the facts relating to living
beings. The more, however, as observation accumulated, and the store
of facts increased, it became difficult for any one man to know the
whole. Hence it has come about that in our own time natural learning
is divided into many distinct provinces, each of which demands a
lifetime of labour from those who would know what has already been
done in the field, and what it is now important to do in the way of
new inquiries.

The large divisions which naturalists have usually made of their tasks
rest in the main on the natural partitions which we may