As just stated, metaphysics and theology are to be avoided. But since Mysticism is generally associated with belief in an Unconditioned Absolute, and since such an Absolute is fatal to the claims of any genuine Nature Mysticism, a preliminary flying incursion into the perilous regions must be ventured. Mysticism in its larger sense is admittedly difficult to define. It connotes a vast group of special experiences and speculations which deal with material supposed to be beyond the reach of sense and reason. It carries us back to the strangely illusive "mysteries" of the Greeks, but is more definitely used in connection with the most characteristic subtleties of the wizard East, and with certain developments of the Platonic philosophy. Extended exposition is not required. Suffice it to state what may fairly be regarded as the three fundamental principles, or doctrines, on which mystics of the orthodox schools generally depend. These principles will be subjected to a free but friendly criticism: considerable modifications will be suggested, and the way thus prepared for the study of Nature Mysticism properly so-called. The three principles alluded to are the following. First, the true mystic is one possessed by a desire to have communion with the ultimately Real. Second, the ultimately Real is to be regarded as a supersensuous, super-rational, and unconditional Absolute-- the mystic One. Third, the direct communion for which the mystic yearns--the _unio mystica_--cannot be attained save by passive contemplation, resulting in vision, insight, or ecstasy. With a view to giving a definite and concrete turn to the critical examination of these three fundamentals, let us take a passage from a recently published booklet. The author tells how that on a certain sunny afternoon he flung himself down on the bank of a brimming mill-stream. The weir was smoothly flowing: the mill-wheel still. He meditates on the scene and concludes thus: "Perhaps we are never so receptive as when with folded hands we say simply, 'This is a great mystery.' I watched and wondered until Jem called, and I had to leave the rippling weir and the water's side, and the wheel with its untold secret." There are certain forms, or modes, of experience here presented which are at least mystical in their tendency--the sense of a deeper reality than that which can be grasped by conscious reason--a desire to penetrate a secret that will not yield itself to articulate thought and which nevertheless leaves a definite impress on the mind. There is also a recognition of the passive attitude which the ordinary mystic doctrine avers to be essential to vision. Will these features warrant our regarding the experiences as genuinely mystical?