Newton's scientific method is a no less important aspect of his work than its results. The _Principia_, in which he gave his discovery to the world, is "a model for all scientific investigations which has never been surpassed." It was, indeed, a brilliant application of the principle of inferring the unknown from the already known, without any dogmatic leaps in the dark. The principle with which he began was that what is true in the narrower spheres of experience (e.g. in the case of an apple falling) is true also in the wider spheres (e.g. in the movements of the celestial bodies). He then made a careful mathematical deduction of what would happen in the case of the planets, assuming that the laws of falling bodies on the earth were applicable to them also. And he concluded by showing that what would happen according to mathematics under this assumption _actually does happen_. The conclusion follows that the same force, i.e. "attraction," operates in both cases. It is no wonder that this final and successful operation was performed by Newton "in a state of excitement so great that he could hardly see his figures." SIGNIFICANCE OF HIS DISCOVERY.--The philosophic importance of the discovery that the motions of the planets may be explained by the "law of gravitation" was twofold. In the first place, it now became possible to understand how the universe held together (a problem which the new astronomy had not solved); and in the second place, the theory constituted a large extension of the mechanical view. It demonstrated that "the physical laws which hold good on the surface of the earth are valid throughout the universe, so far as we can know anything of it." Thus the area of existence in which physical law held good was at once infinitely widened. The mechanical theories of Galileo, Descartes, and others, not only received confirmation, but became more comprehensive than before. So that Newton may be said to have put the finishing touch upon the achievements of his predecessors, and to have crowned their labours with success. And his work has the characteristic of permanency: his "gravitation formula" has stood the test of time. "It still stands there," says a careful and authoritative writer, "as almost the only firmly established mathematical relation, expressive of a property of all matter, to which the progress of more than two centuries has added nothing, and from which it has taken nothing away."[6] RELIGIOUS COROLLARIES.--It would be a profound mistake to assume that the creators of the mechanical view, as it has hitherto met us, were animated by any hostility to religion. Nor did they believe their theories to involve any disastrous consequences in that sphere.