Philosophical Point of View.—But from the philosophical point of view are there objective realities? That is a wider question which throws doubt upon matter itself, and which it is not our place to investigate here. A metaphysician may always discuss and deny the existence of the objective world. It may be maintained that man knows nothing beyond his sensations, and that he only objectivates them and projects them outside himself by a kind of hereditary illusion. We must avoid taking sides in all these difficulties. Physics for the moment ignores them—i.e., postpones their consideration.
In a first approximation we agree to consider ponderable matter only. Chemistry acquaints us with its different forms. They are the different simple bodies, metalloids, metals, and the compound bodies, mineral or organic. Hence we may say that chemistry is the history of the transformations of matter. From the time of Lavoisier this science has followed the transformations of matter, balance in hand, and ascertains that they are accomplished without change of weight.
Law of the Conservation of Matter.—Imagine a system of bodies enclosed in a closed vessel, and the vessel placed in the scale of a balance. All the chemical reactions capable of completely modifying the state of this system have no effect upon the scale of the balance. The total weight is the same before, during, and after. It is precisely this equality of weight which is expressed in all the equations with which treatises on chemistry are filled.
From a higher point of view we recognize here, in this law of Lavoisier or of the conservation of weight, the verification of one of the great laws of nature which we extend to every kind of matter, ponderable or not. It is the law of the conservation of matter, or again, of the indestructibility of matter—“Nothing is lost, nothing is created, all is transformation.” This is exactly what Tait held, this impossibility of creating or destroying matter which at the same time is a proof of its objective existence. This indestructibility of ponderable matter is at the same time the fundamental basis of chemistry. Chemical analysis could not exist if the chemist were not sure that the contents of his vessel at the end of his operations ought to be quantitatively, that is to say by weight, the same as at the beginning, and during the whole course of the experiment.[6]
§ 2. Energy.
The Idea of Energy Derived from the Kinetic Theory.—The notion of energy is not less clear than the notion of matter, it is only more novel to our minds. We are led to it by the mechanical conception which now dominates the whole of physics, the kinetic conception, according to which in the sensible universe there are no phenomena but those of motion. Heat, sound, light, with all their manifestations so complex and so varied, may, according to this theory, be explained by motion. But then, if outside the brain and the mind which has consciousness and which perceives, Nature really offers us only motion, it follows that all phenomena are essentially homogenous among one another, and that their apparent heterogeneity is only the result of the intervention of our sensorium. They differ only in so far as movements are capable of differing—that is to say, in velocity, mass, and trajectory. There is something fundamental which is common to them and this quid commune is energy. Thus the idea of energy may be derived from the kinetic conception, and this is the usual method of exposition.
This method has the great inconvenience of causing an idea which lays claim to reality to depend upon an hypothesis. And besides that, it gives a view of it which may be false. It makes of the different forms of energy something more than varieties which are equivalent to one another. It makes of them one and the same thing. It blends into one the modalities of energy and mechanical energy. For the experimental idea of equivalence, the kinetic theory substitutes the arbitrary idea of the equality, the blending, and the fundamental homogeneity of phenomena. This no doubt is how the founders of energetics, Helmholtz, Clausius, and Lord Kelvin understood things. But a more attentive study and a more scrupulous determination not to go beyond the teaching of experiment should compel us to reform this manner of looking at it. And it is Ostwald’s merit that, after Hamilton, he insisted on this truth—that the various kinds of physical magnitudes furnished by the observation of phenomena are different and characteristic. In particular, we may distinguish among them those which belong to the order of scalar magnitudes and others which are of the order of vector magnitudes.
The Idea of Energy derived from the Connection of Phenomena.—The idea of energy is not absolutely connected with the kinetic theory, and it should not be exposed therefore to the vicissitudes experienced by that theory. It is of a higher order of truth. We can derive it from a less unsafe idea, namely that of the connection of natural phenomena. To conceive it we must get accustomed to this primordial truth, that there are no phenomena isolated in time and space. This statement contains the whole point of view of energetics.
The physics of early days had only an incomplete view of things, for it considered phenomena independently the one of the other.
Phenomena for purposes of analysis were classed in separate and distinct compartments: weight, heat, electricity, magnetism, light. Each phenomenon was studied without reference to that it succeeded or that which should follow. Nothing could be more artificial than such a method as this. In fact, there is a sequence in everything, everything is connected up, everything precedes and succeeds in nature—in nature there are only series. The isolated fact without antecedent or consequent is a myth. Each phenomenal manifestation is in solidarity with another. It is a metamorphosis of one state of things into another. It is transformation. It implies a state of things anterior to that which we are observing, a phenomenal form which has preceded the form of the present moment.