a central truth in which the dispersed rays will again be gathered together.  In fact, all the sciences are working together under the guidance of a principle common to them all, although it may not be consciously known and no attempt is made to define it.  In science, as in philosophy and art and religion, there is a principle of unity, which, though latent, is really prior to all explanation of particular matters of fact.

In truth, man has only one way of knowing.  There is no fundamental difference between scientific and philosophic procedure.  We always light up facts by means of general laws.  The fall of the stone was a perfect enigma, a universally unintelligible bit of experience, till the majestic imagination of Newton conceived the idea of universal gravitation.  Wherever mind successfully invades the realm of chaos, poetry, the sense of the whole, comes first.  There is the intuitive flash, the penetrative glimpse, got no one knows exactly whence—­though we do know that it comes neither from the dead facts nor from the vacant region of a priori thought, but somehow from the interaction of both these elements of knowledge.  After the intuitive flash comes the slow labour of proof, the application of the principle to details.  And that application transforms both the principle and the details, so that the former is enriched with content and the latter are made intelligible—­a veritable conquest and valid possession for mankind.  And in this labour of proof, science and philosophy alike take their share.

Philosophy may be said to come midway between poetry and science, and to partake of the nature of both.  On the one side it deals, like poetry, with ideals of knowledge, and announces truths which it does not completely verify; on the other, it leaves to science the task of articulating its principles in facts, though it begins the articulation itself.  It reveals subsidiary principles, and is, at the same time, a witness for the unity of the categories of science.  We may say, if we wish, that its principles are mere hypotheses.  But so are the ideas which underlie the most practical of the sciences; so is every forecast of genius by virtue of which knowledge is extended; so is every principle of knowledge not completely worked out.  To say that philosophy is hypothetical implies no charge, other than that which can be levelled, in the same sense, against the most solid body of scientific knowledge in the world.  The fruitful question in each case alike is, how far, if at all, does the hypothesis enable us to understand particular facts.

The more careful of our scientific thinkers are well aware of the limits under which they work and of the hypothetical character of their results.  “I take Euclidean space, and the existence of material particles and elemental energy for granted,” says the physicist; “deny them, and I am helpless; grant them, and I shall establish quantitative relations between the different forms of this elemental energy,