entire comprehension, which makes the transparency less complete, and in which the inexplicable shows itself. For the same reason, only few departments of Physics and of Chemistry continue to admit of a mathematical treatment; whereas higher up in the scale of beings this has to be entirely done away with, precisely because of the preponderance of content over form in these phenomena. This content is will, the _à posteriori_, the thing in itself, the free, the causeless. Under the heading "Physiology of Plants," I have shown how--in beings that live and have knowledge--motive and act of will, representation and volition, separate and detach themselves more and more distinctly one from the other, the higher we ascend in the scale of beings. Now, in inorganic Nature also, the cause separates itself from the effect in just the same proportion, and the purely empirical--which is precisely phenomenon of the will--detaches itself more and more prominently; but, just with this, comprehensibility diminishes. This point merits fuller investigation, and I request my readers to give their whole and undivided attention to what I am about to say, as it is calculated to place the leading thought of my doctrine in the strongest possible light, both as to comprehensibility and cogency. But this is all I can do; for it is beyond my power to induce my contemporaries to prefer thoughts to verbiage; I can only console myself for not being the man of the age. On the lowest step of the scale of Nature, cause and effect are quite homogeneous and quite equivalent. Here therefore we have perfect comprehension of the causal connection: for instance, the cause of the movement of one ball propelled by impact, is the movement of another, which loses just as much movement as the first one receives. Here causality is in the highest degree intelligible. What notwithstanding still remains mysterious, is restricted to the possibility of the passage of movement--of a thing incorporeal--from one body to another. The receptivity of bodies in this mode is so slight, that the effect to be produced has to pass over completely from its cause. The same holds good of all purely mechanical influences; and if they are not all just as instantaneously understood, it is either because they are hidden from us by accessory circumstances, or because we are confused by the complicated connection of many causes and effects. In itself, mechanical causality is everywhere equally, that is, in the highest degree, comprehensible; because cause and effect do not differ here as to _quality_, and because where they differ as to _quantity_, as in the lever, mere Space and Time relations suffice to make the thing clear. But as soon as weights come also into play, a second mysterious element supervenes, _gravity_: and, where elastic bodies are concerned, _elasticity_ also.--Things change as soon as we begin to ascend in the scale of phenomena. Heat, considered as cause,