CHEMISTRY OF IDEAS AND SENSATIONS.--Philosophical problems adopt in almost all matters the same form of question as they did two thousand years ago; how can anything spring from its opposite? for instance, reason out of unreason, the sentient out of the dead, logic out of unlogic, disinterested contemplation out of covetous willing, life for others out of egoism, truth out of error? Metaphysical philosophy has helped itself over those difficulties hitherto by denying the origin of one thing in another, and assuming a miraculous origin for more highly valued things, immediately out of the kernel and essence of the "thing in itself." Historical philosophy, on the contrary, which is no longer to be thought of as separate from physical science, the youngest of all philosophical methods, has ascertained in single cases (and presumably this will happen in everything) that there are no opposites except in the usual exaggeration of the popular or metaphysical point of view, and that an error of reason lies at the bottom of the opposition: according to this explanation, strictly understood, there is neither an unegoistical action nor an entirely disinterested point of view, they are both only sublimations in which the fundamental element appears almost evaporated, and is only to be discovered by the closest observation. All that we require, and which can only be given us by the present advance of the single sciences, is a _chemistry_ of the moral, religious, æsthetic ideas and sentiments, as also of those emotions which we experience in ourselves both in the great and in the small phases of social and intellectual intercourse, and even in solitude; but what if this chemistry should result in the fact that also in this case the most beautiful colours have been obtained from base, even despised materials? Would many be inclined to pursue such examinations? Humanity likes to put all questions as to origin and beginning out of its mind; must one not be almost dehumanised to feel a contrary tendency in one's self? 2.