In the dim figure of Pythagoras we perhaps see not only a great leader of physical science, but also a great initiator in spiritual mystery. It is, at any rate, fairly clear that he established religious brotherhoods of carefully selected candidates, women as well as men being eligible, and living on so lofty and aristocratic a level that the populace of Magna Grecia, who could not understand them, decided out of resentment to burn them alive, and the whole order was annihilated about B.C. 500. But exactly how far these early Pythagoreans, whose community has been compared to the mediæval orders of chivalry, were mystics, we may imagine as we list, in the light of the Pythagorean echoes we find here and there in Plato. On the whole we scarcely go to the Greeks for a clear exposition of what we now term “mysticism.” We see more of it in Lucretius than we can divine in his master Epicurus. And we see it still more clearly in the Stoics. We can, indeed, nowhere find a more pure and concise statement than in Marcus Aurelius of the mystical core of religion as the union in love and harmony and devotion of the self with the Not-Self. If Lucretius may be accounted the first of moderns in the identification of mysticism and science, he has been followed by many, even though, one sometimes thinks, with an ever-increasing difficulty, a drooping of the wings of mystical aspiration, a limping of the feet of scientific progress. Leonardo and Giordano Bruno and Spinoza and Goethe, each with a little imperfection on one side or the other, if not on both sides, have moved in a sphere in which the impulses of religion are felt to spring from the same centre as the impulses of science. Einstein, whose attitude in many ways is so interesting, closely associates the longing for pure knowledge with religious feeling, and he has remarked that “in every true searcher of Nature there is a kind of religious reverence.” He is inclined to attach significance to the fact that so many great men of science—Newton, Descartes, Gauss, Helmholtz—have been in one way or another religious. If we cannot altogether include such men as Swedenborg and Faraday in the same group, it is because we cannot feel that in them the two impulses, however highly developed, really spring from the same centre or really make a true harmony. We suspect that these men and their like kept their mysticism in a science-proof compartment of their minds, and their science in a mysticism-proof compartment; we tremble for the explosive result, should the wall of partition ever be broken down.