We might express all this by saying that Imagination is the mother of working-hypotheses; and this is true of all working-hypotheses, those of the observatory and laboratory as well as those of the nursery. No one who grasps this truth will henceforth deny the debt of science to Imagination. Knowledge is not worth calling knowledge till it is reduced to Law; and Law, as I have shown you above, is a mere idea of the Imagination. I do not deny the subsequent value of Reason; but Imagination must come first. It was from the Imagination that there first flashed upon the mind of Newton the vision of the working-hypothesis by which the apple’s fall and the planet’s path might be simultaneously explained. Then came in Reason, with experiment, testing, comparing, prepared to detect discrepancies, unlikelihoods, and any want of harmony between the new theory and the old order of things. Finally, the once-no-more-than-working-hypothesis, having been found to harmonize with countless past and present phenomena and having enabled us to predict countless future phenomena, is now called a Law, and we are practically certain that it will act. The approval of this Law we owe to Reason, but for the suggestion of it we are indebted to Imagination. On the debt owed to Imagination by Mathematics—the foundation of all science—I will not add anything to what has been said in a recent letter. Next as to the work of Imagination in art. Poets and artists, as well as astronomers, must be, so to speak, _ex analogia Universi_; that is to say, they must be in harmony with that order of things which they long to reveal to their fellow-men; they must see Law and Unity where others fail to see it; they must have inherited or received capacities and intuitions which give them an intense sympathy with the deep-down-hidden rhythms and abysmal motions which regulate atoms and sounds and hues and shapes, and the thoughts and feelings of men. An artist who wishes to paint a hill-side, or a wave, or a face, must have a vision of it. He must see it not only exactly as it is, but how it is: he sympathizes, as it were, with every cleft and runlet and hollow and projection of the hill, with every turn and fold and shade and hue of the ever-varying wave: he realizes the secret of Nature’s working. Shall we make a distinction between the secret in the one case and the other? Shall we say the “spirit” of the face, but the “law” of the hill and the “law” of the wave? Or will not the intuition into this complex combination of multitudinous forces, apparently free and conflicting yet all guided and controlled into one harmonious result, be better expressed by saying that he enters into the “spirit” in all cases, the “spirit” of the hill, the wave, and the face? In proportion as he has this power, a great artist will be less likely to speak about it, and less able to explain it: but have it he must; and it is a power really not dissimilar, though