'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 limited by its author to the Physical Sciences only. In addition to this circumscribed application, it is moreover indistinct by reason of the use of the word Ideas, a word to which so many different significations have been attached by different writers that its meaning is vague and undefined--to convey the impression of Laws or Principles. The same defect exists in the detailed exposition is perhaps the most extended and complete extant. But even when we gain a clear conception of the proposition which Professor Whewell only vaguely apprehends and therefore does not clearly state, namely--that Science is an assemblage of Facts correlated by Laws or Principles, a system in which the mutual _relations_ of the Facts are known, and the Laws or Principles established by them are discovered;--when we understand this ever so distinctly, we are still at the beginning of a knowledge of what constitutes Science. When do we know that we have a Fact? How are we to be sure that our proof is not defective? By what means shall it be certain, beyond the cavil of a doubt, that the right Laws or Principles, and no more than those warranted by the Facts, are deduced? These and some other questions must be definitely settled before we can thoroughly comprehend the nature of Science, and the consideration of which brings us, in the first place, to the examination of the characteristics of Scientific Methods.