Who builds defences for that which is impregnable or little likely to be assailed? The answer is ready, that unless the defences had been built in former times it would be impossible to do without them now; but this does not touch the argument, which is not that demonstration is unwise, but that as long as a demonstration is still felt necessary, and therefore kept ready to hand, the subject of such demonstration is not yet securely known. _Qui s’excuse_, _s’accuse_; and unless a matter can hold its own without the brag and self-assertion of continual demonstration, it is still more or less of a parvenu, which we shall not lose much by neglecting till it has less occasion to blow its own trumpet. The only alternative is that it is an error in process of detection, for if evidence concerning any opinion has long been denied superfluous, and ever after this comes to be again felt necessary, we know that the opinion is doomed. If there is any truth in the above, it should follow that our conception of the words “science” and “scientific” should undergo some modification. Not that we should speak slightingly of science, but that we should recognise more than we do, that there are two distinct classes of scientific people corresponding not inaptly with the two main parties unto which the political world is divided. The one class is deeply versed in those sciences which have already become the common property of mankind; enjoying, enforcing, perpetuating, and engraving still more deeply unto the mind of man acquisitions already approved by common experience, but somewhat careless about extension of empire, or at any rate disinclined, for the most part, to active effort on their own part for the sake of such extension—neither progressive, in fact, nor aggressive—but quiet, peaceable people, who wish to live and let live, as their fathers before them; while the other class is chiefly intent upon pushing forward the boundaries of science, and is comparatively indifferent to what is known already save in so far as necessary for purposes of extension. These last are called pioneers of science, and to them alone is the title “scientific” commonly accorded; but pioneers, unimportant to an army as they are, are still not the army itself; which can get on better without the pioneers than the pioneers without the army. Surely the class which knows thoroughly well what it knows, and which adjudicates upon the value of the discoveries made by the pioneers—surely this class has as good a right or better to be called scientific than the pioneers themselves.