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within which alone its action is really confined. An attempt has been made to base a formal division of knowledge upon it. We have already gone so far in this direction that there are whole departments of machine construction scarcely intelligible to each other. For a practical mechanician to know something of those regions of intellectual life which lie beyond the industrial circle has become rare. Yet nothing can be more certain than that the endless isolation of efforts must be detrimental to the whole. This division of knowledge cannot be carried further without harm ; it is rather our duty to join together once more the sundered depart- ments, resting their connection upon a higher unity, and so bringing to view the real scope and purpose of the whole. The sense of the community of human efforts should find expression not merely in the scientific consciousness of individuals, but also in the form in which the perceptions are cultivated and extended.
The idea upon which the foregoing sketch of the growth of machinery has been founded, the very notion of development, does in itself act powerfully to strengthen this sense. All our later investigations have made this idea more or less their own, in the region of historical research as well as in that of natural history, into which it has infused such life. It alone both demands and renders possible the looking at a whole department really as a whole. It compels a far-reaching view, a looking beyond the present time and place it at once deepens and heightens the comprehension of single phenomena. It has given to the science of to-day a power which could scarcely have been imagined two generations ago. To the inquirer at that time a series of phe- nomena was a series of isolated facts ; the order in which they arranged themselves was only that of a string of pearls, the casual connection between them was nothing more than the thread which tied them togther. To-day, on the other hand, we look upon this same causal connection of thoughts, with their growth and unbroken flow, as that which is most essential ; we see in it not so much the thing which links phenomena together as that to which they owe their very life and being.
I have attempted to place this antithesis before the reader in the two mottoes which head this chapter. Between the sentences of Schiller and of Geiger lies the deep contrast between the former spirit and the present. The passage from Schiller, interesting
