lear conception of what constitutes _knowledge_, of where the dividing
line between it and opinion lay, departments of the universe of
intelligence almost wholly wanting in exactness and certainty have been
dignified with the same title which we apply to departments most
positively _known_. We hear of the Science of Mathematics, the Science
of Chemistry, the Science of Medicine, the Science of Political Economy,
and even of the Science of Theology.

This vague use of the word Science is not confined to general custom
only, but appertains as well to Scientists and writers on scientific
subjects. So general is this indistinct understanding of the meaning of
this term, that there does not exist in the range of scientific
literature a precise, compact, exhaustive, intelligible definition of
it. In order, therefore, to approach our present subject with clear
mental vision, we must gain an accurate conception of the character and
constituents of Science.

In his _History of the Inductive Sciences_, Professor Whewell says:

'In the first place, then, I remark, that to the formation of
science, two things are requisite:--Facts and Ideas; observation of
Things without, and an inward effort of Thought; or, in other
words, Sense and Reason. Neither of these elements, by itself, can
constitute substantial general knowledge. The impression of sense,
unconnected by some rational and speculative principle, can only
end in a practical acquaintance with individual objects; the
operations of the rational faculties, on the other hand, if allowed
to go on without a constant reference of external things, can lead
only to empty abstraction and barren ingenuity. Real speculative
knowledge demands the combination of the two ingredients--right
reason and facts to reason upon. It has been well said, that true
knowledge is the interpretation of nature; and therefore it
requires both the interpreting mind, and nature for its subject,
both the document, and ingenuity to read it aright. Thus invention,
acuteness, and connection of thought, are necessary on the one
hand, for the progress of philosophical knowledge; and on the other
hand, the precise and steady application of these faculties to
facts well known and clearly conceived.'

This explanation of the nature of Science, more elaborately expanded in
_The Philosophy of the Inductive Sciences_, is li