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 powers of one man or one generation, he left to posterity the work of filling in the framework which he had designed. Descartes, on the other hand, desired to leave as little as possible for his successors to do; his was a theory of the universe, worked out as far as possible in every detail. It is, however, impossible to derive such a theory inductively unless there are at hand sufficient observational data on which to base the induction; and as such data were not available in the age of Descartes, he was compelled to deduce phenomena from preconceived principles and causes, after the fashion of the older philosophers. To the inherent weakness of this method may be traced the errors that at last brought his scheme to ruin.

The contrast between the systems of Bacon and Descartes is not unlike that between the Roman republic and the empire of Alexander. In the one case we have a career of aggrandizement pursued with patience for centuries; in the other a growth of fungus-like rapidity, a speedy dissolution, and an immense influence long exerted by the disunited fragments. The grandeur of Descartes' plan, and the boldness of its execution, stimulated scientific thought to a degree before unparalleled; and it was largely from its ruins that later philosophers constructed those more valid theories which have endured to our own time.

Descartes regarded the world as an immense machine, operating by the motion and pressure of matter. “Give me matter and motion," he cried, "and I will construct the universe." A peculiarity which distinguished his system from that which afterwards sprang from its decay was the rejection of all forms of action at a distance; he assumed that force cannot be communicated except by actual pressure or impact. By this assumption he was compelled to provide an explicit mechanism in order to account for each of the known forces of nature—a task evidently much more difficult than that which lies before those who are willing to admit action at a distance as an ultimate property of matter.

Since the sun interacts with the planets, in sending them B2