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[ Theosophical System of Nature. Of all the modern attempts of dualistic philosophy to establish the knowledge of nature on a theological basis (that of Christian monotheism), the Essay on Classification of Louis Agassiz is by far the most important,—in strictness, indeed, is the only one worthy of mention. (On this see my Natural History of Creation, Lect. III., also "Aims and Methods of the Modern Embryology," 1875, Jena Zeitschr. für Naturw., Bd. x., Supplement.)]
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[ Darwin and Copernicus. This is the title of an address delivered by Du Bois-Reymond on 25th January 1883, in the Berlin Academy of Sciences, and afterwards published in his Collected Addresses (vol. ii. 1887). As the author himself mentions in a note (p. 500) that this gave rise, "most unmeritedly," to great excitement, and called down upon him the violent attacks of the clerical press, I may be allowed to point out here that it contained nothing new, I myself, fifteen years previously, in my lectures on "The Origin and Genealogy of the Human Race," having carried out in detail the comparison between Darwin and Copernicus, and the service rendered by these two heroes in putting an end to the anthropocentric and geocentric views of the world. (See the Third Series in Virchow and Holtzendorff's Collection of Popular Scientific Lectures, Nos. 53 and 54, 1868, 4th ed., 1881.) When Du Bois-Reymond says, "For me, Darwin is the Copernicus of the organic world," I am the more pleased to find that he agrees (partly in identical words) with my way of thinking, as he himself, quite unnecessarily, takes up an attitude of opposition towards me. The same is the case with regard to the explanation of innate ideas by Darwinism, which he has attempted in his address (1870) on "Leibnitzian Ideas in Modern Science" (vol. i. of the Collected Addresses). Here also he is most agreeably at one with me in what, four years before, I had elaborated in my General Morphology (vol. ii. p. 446), and in my Natural History of Creation (1868). "The laws of heredity and adaptation explain to us how it is that à priori ideas have been developed out of what was originally à posteriori knowledge," etc. I cannot fail to be highly flattered in being able in these last days to greet the renowned orator of the Berlin Academy as a friend and patron of the Natural History of Creation, which he had previously designated a bad romance. But his winged words are not on that account to be forgotten, that "the genealogical trees of phylogeny are about as much worth as, in the eyes of the historical critic, are those of the Homeric heroes" (Darwin versus Galiani, 1876).]
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[ The Law of the Conservation of Substance. Strictly taken, this belongs also to "scientific articles of faith," and could stand as the first article of our "monistic religion." Physicists of the present day, it is true, generally (and correctly) regard their "law of the conservation of energy" as the immovable foundation of all their science (Robert Mayer, Helmholtz), just as in like manner chemists so regard their fundamental law of the "conservation of matter" (Lavoisier). Sceptical philosophers could, however, raise certain objections to either of these fundamental laws with as much success as against their combination into the single superior law of the "conservation of substance." As a matter of fact, dualistic philosophy still attempts to raise such objections, often under the guise of cautious criticism. The sceptical (in part also purely dogmatic) objections have a semblance of justification only in so far as they relate to the fundamental problem of substance, the primary question as to the connection between matter and energy. While freely recognising the presence of this real "boundary of natural knowledge," we can yet, within this boundary, apply quite universally the "mechanical law of causality." The complicated "phenomena of mind," as they are called (more especially consciousness), fall under the "law of the conservation of substance" just as strictly as do the simpler mechanical processes of nature dealt with in inorganic physics and chemistry. Compare note 16.]
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[ Kant and Monism. As recent German philosophy has in a large measure returned to Kant, and in some cases even deified as "infallible" the great Königsberg philosopher, it may be well here to point out once more that his system of critical philosophy is a mixture of monistic and dualistic ingredients. His critical principles of the theory of knowledge will always remain of fundamental importance: his proof that we are unable to know the essential and profoundest essence of substance, the "thing in itself" (or "the combination of matter and energy"); that our knowledge remains subjective in its nature; that it is conditioned by the organisation of our brain and sensory organs, and can therefore only deal with the phenomena which our experience of the outer world affords us. But within these "limits of human knowledge" a positive monistic knowledge of nature is still possible, in contrast to all dualistic and metaphysical fantasies. One such great fact of monistic knowledge was the mechanical cosmogony of Kant and Laplace, the "Essay on the Constitution and Mechanical Origin of the Universe, according to the Principles of Newton" (1755). In the whole field of our knowledge of inorganic nature, Kant held firmly to the monistic point of view, allowing mechanism alone as the real explanation of the phenomena. In the science of organic nature also, on the other hand, he held monism to be valid indeed, yet insufficient; here he considered it necessary to call in the aid of final as well as of efficient causes. (Cf. the fifth lecture of my Natural History of Creation on "The Evolution-Theory of Kant and Lamarck"; also Albrecht Rau's Kant und die Naturforschung: Eine Prüfung der Resultate des idealistischen Kritikismus durch den realistischen Kosmos, vol. ii., 1886.) Once thus on the downgrade of dualistic teleology, Kant afterwards arrived at his untenable metaphysical views of "God, Freedom, and Immortality." It is probable that Kant would have escaped these errors if he had had a thorough anatomical and physiological training. The natural sciences were, indeed, at that time truly in their infancy. I am firmly convinced that Kant's system of critical philosophy would have turned out quite otherwise from what it was, and purely monistic, if he had had at his disposal the then unsuspected treasures of empirical natural knowledge which we now possess.]
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[ The Ether. In a thoughtful lecture on the relations between light and electricity at the sixty-second Congress of German naturalists and physicians in Heidelberg in 1889, Heinrich Hertz explains the scope of his brilliant discovery: "Thus the domain of electricity extends over the whole of nature. It comes nearer to ourselves; we learn that we actually possess an electric organ, the eye. Here we are brought face to face with the question as to unmediated actio in distans. Is there such a thing? Not far off from this, in another direction, lies the question of the nature of electricity. And immediately connected therewith arises the momentous and primary question as to the nature of the ether, of the properties of the medium that fills all space, its structure, its rest or motion, its infinitude or finitude. It becomes every day more manifest that this question rises above all others, that a knowledge of what the ether is would reveal to us not only the nature of the old 'imponderables,' but also of the old 'matter' itself and its most essential properties, weight and inertia. Modern physics is not far from the question whether everything that exists is not created from the ether." This question is already being answered in the affirmative by some monistic physicists, as, for example, by J. G. Vogt in his most suggestive work on The Nature of Electricity and Magnetism, on The Basis of the Conception of a Single Substance (Leipsic, 1891). He regards the atoms of mass (the primal atoms of the kinetic theory of matter) as individualised centres of concentration of the continuous substance that uninterruptedly fills all space; the mobile elastic part of this substance between the atoms, and universally distributed, is—the ether. Georg Helm in Dresden, on the basis of mathematico-physical experiments, had already at an earlier date arrived at the same conclusions; in his treatise on "Influences at a Distance mediated by the Ether" (Annalen der Physik und Chemie, 1881, Bd. xiv.), he shows that it requires only the postulate of one particular kind of matter, the ether, to explain influence at a distance and radiation; that is, as regards these phenomena, all the qualities ascribable to matter, except that of motion, are of no account; in other words, that in thinking of the ether we simply require to think of it as "the mobile.">[