10. This conclusion, however, was very slowly reached. The distinction of aspects was made the ground of a corresponding distinction in agencies. Each group was personified and isolated. The one group was personified in Spirit--an existent in every respect opposed to Matter, which was the existent represented in the other group. One was said to be simple, indestructible; the other compound, destructible. One was invisible, impalpable, beyond the grasp of Sense; the other was visible, tangible, sensible. One was of heaven, the other of earth. Thus a biological Dualism, analogous to the cosmological, replaced the First Notion. It was undermined by advances in two directions. Psychology began to disclose that our conception of Matter was, to say the least, _saturated_ with Mind, its Atoms confessedly being ideal figments; and that all the terms by which we expressed _material qualities_ were terms which expressed _modes of Feeling_; so that whatever remained over and above this was the unknown _x_, which speculation required as a postulate. Idealism, rejecting this postulate, declared that Matter was simply the projection of Mind, and that our Body was the objectivation of our Soul. Physiology began to disclose that all the mental processes were (mathematically speaking) _functions_ of physical processes, i. e. varying with the variations of bodily states; and this was declared enough to banish forever the conception of a Soul, except as a term simply expressing certain functions.