For my part, I am convinced of the profound importance of the unifying “law of substance,” as an expression of the inseparable connection in reality of two laws which are only separated in conception. That they were not originally taken together and their unity recognized from the beginning is merely an accident of the date of their respective discoveries. The earlier and more accessible chemical law of the persistence of matter was detected by Lavoisier in 1789, and, after a general application of the balance, became the basis of exact chemistry. On the other hand, the more recondite law of the persistence of force was only discovered by Mayer in 1842, and only laid down as the basis of exact physics by Helmholtz. The unity of the two laws—still much disputed—is expressed by many scientists who are convinced of it in the formula: “Law of the persistence of matter and force.” In order to have a briefer and more convenient expression for this fundamental thought, I proposed some time ago to call it the “law of substance” or the “fundamental cosmic law”; it might also be called the “universal law,” or the “law of constancy,” or the “axiom of the constancy of the universe.” In the ultimate analysis it is found to be a necessary consequence of the principle of causality.[24]
The first thinker to introduce the purely monistic conception of substance into science and appreciate its profound importance was the great philosopher Baruch Spinoza; his chief work appeared shortly after his premature death in 1677, just one hundred years before Lavoisier gave empirical proof of the constancy of matter by means of the chemist’s principal instrument, the balance. In his stately pantheistic system the notion of the world (the universe, or the cosmos) is identical with the all-pervading notion of God; it is at one and the same time the purest and most rational monism and the clearest and most abstract monotheism. This universal substance, this “divine nature of the world,” shows us two different aspects of its being, or two fundamental attributes—matter (infinitely extended substance) and spirit (the all-embracing energy of thought). All the changes which have since come over the idea of substance are reduced, on a logical analysis, to this supreme thought of Spinoza’s; with Goethe I take it to be the loftiest, profoundest, and truest thought of all ages. Every single object in the world which comes within the sphere of our cognizance, all individual forms of existence, are but special transitory forms—accidents or modes—of substance. These modes are material things when we regard them under the attribute of extension (or “occupation of space”), but forces or ideas when we consider them under the attribute of thought (or “energy”). To this profound thought of Spinoza our purified monism returns after a lapse of two hundred years; for us, too, matter (space-filling substance) and energy (moving force) are but two inseparable attributes of the one underlying substance.
Among the various modifications which the fundamental idea of substance has undergone in modern physics, in association with the prevalent atomism, we shall select only two of the most divergent theories for a brief discussion, the kinetic and the pyknotic. Both theories agree that we have succeeded in reducing all the different forces of nature to one common original force; gravity and chemical action, electricity and magnetism, light and heat, etc., are only different manifestations, forms, or dynamodes, of a single primitive force (prodynamis). This fundamental force is generally conceived as a vibratory motion of the smallest particles of matter—a vibration of atoms. The atoms themselves, according to the usual “kinetic theory of substance,” are dead, separate particles of matter, which dance to and fro in empty space and act at a distance. The real founder and most distinguished representative of the kinetic theory is Newton, the famous discoverer of the law of gravitation. In his great work, the Philosophiae Naturalis Principia Mathematica (1687), he showed that throughout the universe the same law of attraction controls the unvarying constancy of gravitation; the attraction of two particles being in direct proportion to their mass and in inverse proportion to the square of their distance. This universal force of gravity is at work in the fall of an apple and the tidal wave no less than in the course of the planets round the sun and the movements of all the heavenly bodies. Newton had the immortal merit of establishing the law of gravitation and embodying it in an indisputable mathematical formula. Yet this dead mathematical formula, on which most scientists lay great stress, as so frequently happens, gives us merely the quantitative demonstration of the theory; it gives us no insight whatever into the qualitative nature of the phenomena. The action at a distance without a medium, which Newton deduced from his law of gravitation, and which became one of the most serious and most dangerous dogmas of later physics, does not afford the slightest explanation of the real causes of attraction; indeed, it long obstructed our way to the real discovery of them. I cannot but suspect that his speculations on this mysterious action at a distance contributed not a little to the leading of the great English mathematician into the obscure labyrinth of mystic dreams and theistic superstition in which he passed the last thirty-four years of his life; we find him, at the end, giving metaphysical hypotheses on the predictions of Daniel and on the paradoxical fantasies of St. John.
In fundamental opposition to the theory of vibration, or the kinetic theory of substance, we have the modern “theory of condensation,” or the pyknotic theory of substance. It is most ably established in the suggestive work of J. C. Vogt on The Nature of Electricity and Magnetism on the Basis of a Simplified Conception of Substance (1891). Vogt assumes the primitive force of the world, the universal prodynamis, to be, not the vibration or oscillation of particles in empty space, but the condensation of a simple primitive substance, which fills the infinity of space in an unbroken continuity. Its sole inherent mechanical form of activity consists in a tendency to condensation or contraction, which produces infinitesimal centres of condensation; these may change their degree of thickness, and, therefore, their volume, but are constant as such. These minute parts of the universal substance, the centres of condensation, which might be called pyknatoms, correspond in general to the ultimate separate atoms of the kinetic theory; they differ, however, very considerably in that they are credited with sensation and inclination (or will-movement of the simplest form), with souls, in a certain sense—in harmony with the old theory of Empedocles of the “love and hatred of the elements.” Moreover, these “atoms with souls” do not float in empty space, but in the continuous, extremely attenuated intermediate substance, which represents the uncondensed portion of the primitive matter. By means of certain “constellations, centres of perturbation, or systems of deformation,” great masses of centres of condensation quickly unite in immense proportions, and so obtain a preponderance over the surrounding masses. By that process the primitive substance, which in its original state of quiescence had the same mean consistency throughout, divides or differentiates into two kinds. The centres of disturbance, which positively exceed the mean consistency in virtue of the pyknosis or condensation, form the ponderable matter of bodies; the finer, intermediate substance, which occupies the space between them, and negatively falls below the mean consistency, forms the ether, or imponderable matter. As a consequence of this division into mass and ether there ensues a ceaseless struggle between the two antagonistic elements, and this struggle is the source of all physical processes. The positive ponderable matter, the element with the feeling of like or desire, is continually striving to complete the process of condensation, and thus collecting an enormous amount of potential energy; the negative, imponderable matter, on the other hand, offers a perpetual and equal resistance to the further increase of its strain and of the feeling of dislike connected therewith, and thus gathers the utmost amount of actual energy.
We cannot go any further here into the details of the brilliant theory of J. C. Vogt. The interested reader cannot do better than have recourse to the second volume of the above work for a clear, popular exposition of the difficult problem. I am myself too little informed in physics and mathematics to enter into a critical discussion of its lights and shades; still, I think that this pyknotic theory of substance will prove more acceptable to every biologist who is convinced of the unity of nature than the kinetic theory which prevails in physics to-day. A misunderstanding may easily arise from the fact that Vogt puts his process of condensation in explicit contradiction with the general phenomenon of motion; but it must be remembered that he is speaking of vibratory movement in the sense of the physicist. His hypothetical “condensation” is just as much determined by a movement of substance as is the hypothetical “vibration”; only the kind of movement and the relation of the moving elements are very different in the two hypotheses. Moreover, it is not the whole theory of vibration, but only an important section of it, that is contradicted by the theory of condensation.
Modern physics, for the most part, still firmly adheres to the older theory of vibration, to the idea of an actio in distans and the eternal vibration of dead atoms in empty space; it rejects the pyknotic theory. Although Vogt’s theory may be still far from perfect, and his original speculations may be marred by many errors, yet I think he has rendered a very good service in eliminating the untenable principles of the kinetic theory of substance. As to my own opinion—and that of many other scientists—I must lay down the following theses, which are involved in Vogt’s pyknotic theory, as indispensable for a truly monistic view of substance, and one that covers the whole field of organic and inorganic nature:
I. The two fundamental forms of substance, ponderable matter and ether, are not dead and only moved by extrinsic force, but they are endowed with sensation and will (though, naturally, of the lowest grade); they experience an inclination for condensation, a dislike of strain; they strive after the one and struggle against the other.
II. There is no such thing as empty space; that part of space which is not occupied with ponderable atoms is filled with ether.
III. There is no such thing as an action at a distance through perfectly empty space; all action of bodies upon each other is either determined by immediate contact or is effected by the mediation of ether.