The order of the outcome of the sciences in time, therefore, and their connexions with one another, cannot be explained or understood, if we look only to the sciences themselves. We must first of all descend into the depths of natural thought, or of general culture, and trace the lines which unite science with science in that general medium. The systematic interdependence of the sciences must be chiefly sought for in the workings of thought as a whole in its popular phases, and in the action and reaction of that _general_ human thought with the sciences, those definite organisations of knowledge which form sporadically round the _nuclei_ here and there presented in what would superficially be described as the inorganic mass and medium of popular knowledge. Thus, by means of the sciences in their aggregate action, the material of common consciousness is expanded and developed, at least in certain parts, though the expansion may be neither consistent nor systematic. But so long as this work is incomplete, so long, that is to say, as every point in the line of popular knowledge has not received its due elaboration and equal study, the sciences merely succeed each other in a certain imperfect sequence, or exist in juxtaposition: they do not form a total. The whole of scientific knowledge will only be formed, when science shall be as completely rounded and unified, as in its lower sphere and more inadequate element the ordinary consciousness of the world is now. Up to a certain point the method of science is but the method of ordinary consciousness pursued knowingly and steadily. But ere long the method acquires a distinctive character of its own. It shakes off the pressure of that immediate subservience in which ordinary knowledge stands to man's needs, wishes and interests. Knowledge is pursued--within a wide range--for its own sake, and by a class more or less definitely set apart by humanity for its scientific service,--which is thus performed more systematically and continuously. But the great step which carries ordinary knowledge into its higher region is the discovery, due to reflection and comparison, that there is a double grade of reality-a permanent, essential, uniform, substantial being, which is contrasted with an evanescent, apparent, varying and accidental. To know a thing is in all cases to _relate it_ to something else: to know it in the higher sense_--vere scire_--is to relate it to its essence, its substantial or universal form, its permanent self. Ordinary knowledge, e. g., fixes a thing by referring to its antecedents: scientific knowledge refers it to its 'invariable, 'unconditional' or 'essential' antecedent,--to something which contains it implicitly, and necessarily, and is not merely by accident or juxtaposition associated with it. To discover this permanent, underlying substance or reality comes to be the problem of science--a problem which may be taken in the widest generality, or restricted