The word _Science_ has been so indiscriminately applied to very diverse departments of our intellectual domain, that it has ceased to have any distinctive or well-defined signification. Meaning, appropriately, that which is certainly _known_, as distinguished from that which is matter of conjecture, opinion, thought, or plausible supposition merely, its application to any special branch of human inquiry signifies, in that sense, that the facts and principles relating to the given branch, or constituting it, are no longer subjects of uncertain investigation, but have become accurately and positively _known_, so as to be demonstrable to all intelligent minds and invariably recognized by them as true when rightly apprehended and understood. In the absence, however, of any clear 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: