paper on "Materialism," contributed apparently as a part of a series of "Philosopliical Researches" to the periodical "Atlantis" in 1855; a memorial address on Alexander von Humboldt (1859); the earlier papers of the "Concepts," which were published in "The Popular Science Monthly" in 1873 and 1874; and a "Reply to some Criticisms on the 'Concepts,'" in a later number. In introducing the first of the articles in the "Monthly" (October, 1873), which was on "The Theory of the Atomic Constitution of Matter," the editor of this journal, Prof. E. L. Youmans, said, "The depth and force of the criticism are only equaled by the clearness of the conceptions and the precision and felicity of the statement."
This work is a thoroughgoing criticism of the theories and concepts by which modern scientific philosophy seeks to coordinate the facts of physics, chemistry, and astronomy. In the main this philosophy assumes all phenomena to be reducible to mechanics, and holds that the ultimate elements at which physical analysis arrives are mass and motion; the physical unit being an atom, hard, inelastic, inert, and passive. Since the concept of atoms defines them as absolutely simple, it follows that they must of necessity be equal. Yet here chemistry at once speaks in contradiction, for the atoms, or units, currently so named, differ radically in properties and characteristics. In a review of modern theories of the phases of energy, or modes of motion, we are shown the difficulties which attend the assumption of an ether as the vehicle whereby radiant energy is transferred. From the instantaneous propagation of gravitation through space, it is argued that no medium whatever may be needful for its communication. The kinetic theory of gases is next examined, which theory is shown to involve greater difficulties than it clears up. Next in order the author proceeds to define the conditions of true hypothesis, which in his view should both accord with all known facts and simplify them. He shows how modern theorists have neglected this canon, and supposed they were explaining a fact when they were only dwarfing it, or stating it in new terms. He finds more difficulty in understanding an atom than the mass which it goes to make up.
No portion of the "Concepts" is more striking than its chapter on the relation of thought to things. We are pointed to the fallacy which makes mind the measure of nature, and conceivability the test of truth. The author demonstrates how the historical order in which human knowledge has arisen has largely molded scientific conceptions—for example, in its being supposed that the solid form of matter, the first known and most familiar, is more simple than the gaseous. And because impact is the common mode of propagating motion, ideas as to the propagation of