not, if, on the contrary, each science is ruled by its own hypothesis,
and uses that hypothesis to bind its facts together, then the question
arises, are there no wider colligating principles amongst these
hypotheses themselves? Are the sciences independent of each other, or
is their independence only surface appearance? This is the question
which philosophy asks, and the sciences themselves by their progress
suggest a positive answer to it.

The knowledge of the world which the sciences are building is not a
chaotic structure. By their apparently independent efforts, the outer
kosmos is gradually reproduced in the mind of man, and the temple of
truth is silently rising. We may not as yet be able to connect wing with
wing, or to declare definitely the law of the whole. The logical order
of the hypotheses of the various sciences, the true connection of these
categories of constructive thought, may yet be uncertain. But, still,
there _is_ such an order and connection: the whole building has its
plan, which becomes more and more intelligible as it approaches to its
completion. Beneath all the differences, there are fundamental
principles which give to human thought a definite unity of movement and
direction. There are architectonic conceptions which are guiding, not
only the different sciences, but all the modes of thought of an age.
There are intellectual media, "working hypotheses," by means of which
successive centuries observe all that they see; and these far-reaching
constructive principles divide the history of mankind into distinct
stages. In a word, there are dynasties of great ideas, such as the idea
of development in our own day; and these successively ascend the throne
of mind, and hold a sway over human thought which is well-nigh absolute.

Now, if this is so, is it certain that all _knowledge_ of these ruling
conceptions is impossible? In other words, is the attempt to construct a