By the atomic theory, we do not gain anything for the ultimate explanation of the world and its contents, not even if its present hypothetical value should be changed into a complete demonstration. For the whole theory but removes the question as to the origin of things from their sensible appearance to the elements of that appearance, and leaves us standing just as helpless before the elements as before the appearances. For {145} whence does the whole richness of the appearances in the world come? If the atoms are all alike, and their laws of force the simplest we can imagine, then their grouping into all the developments and formations of which we observe such an infinite and regularly arranged abundance, is not less unexplained than if we had not gone back to the theory of atoms at all. But if the atoms and their laws of force are different, the difficulty is not simplified, but doubled. For, first, the theory then owes us an answer to the questions wherein the difference of the atoms consists and whence it comes; and, second, the question we have to consider in supposing a uniformity of the atoms, is not disposed of or answered--the question, namely, as to the causes which bring these different atoms together to form precisely those complexities of atoms which we observe as the world of phenomena. This insufficiency of the theory of atoms in explaining the world and its contents, is another proof to us that, however great the practical value of this theory may be for the operations of physics and chemistry, its theoretical value consists essentially in the fact that it formulates more accurately the perception of the limits of our exact knowledge. Even the idea of Lotze, that the atoms (in themselves different) are not really the final elements of matter, but consist of still more simple but likewise different elements, seems to us more a decoration than an extension of the limits at which our perception has arrived; we stand before a double door, but find both doors locked. We agree with DuBois-Reymond, when he declares, in his before-mentioned lecture, the impossibility of perceiving the last elements of the {146} world, matter and force, to be the other limit of our knowledge of nature which, together with the impossibility of the explanation of the origin of sensation and consciousness, remains forever fixed.