[65] It is clear from this that all so-called elementary (differential) laws involve a relation to the whole.
[66] If it be objected, that in the case of perturbations of the velocity of rotation of the earth, we could be sensible of such perturbations, and being obliged to have some measure of time, we should resort to the period of vibration of the waves of sodium light,—all that this would show is that for practical reasons we should select that event which best served us as the simplest common measure of the others.
[67] Measurement, in fact, is the definition of one phenomenon by another (standard) phenomenon.
[68] I have represented the point of view here taken for more than thirty years and developed it in various writings (Erhaltung der Arbeit, 1872, parts of which are published in the article on The Conservation of Energy in this collection; The Forms of Liquids, 1872, also published in this collection; and the Bewegungsempfindungen, 1875). The idea, though known to philosophers, is unfamiliar to the majority of physicists. It is a matter of deep regret to me, therefore, that the title and author of a small tract which accorded with my views in numerous details and which I remember having caught a glance of in a very busy period (1879-1880), have so completely disappeared from my memory that all efforts to obtain a clue to them have hitherto been fruitless.
[69] Inaugural Address, delivered on assuming the Rectorate of the University of Prague, October 18, 1883.
The idea presented in this essay is neither new nor remote. I have touched upon it myself on several occasions (first in 1867), but have never made it the subject of a formal disquisition. Doubtless, others, too, have treated it; it lies, so to speak, in the air. However, as many of my illustrations were well received, although known only in an imperfect form from the lecture itself and the newspapers, I have, contrary to my original intention, decided to publish it. It is not my intention to trespass here upon the domain of biology. My statements are to be taken merely as the expression of the fact that no one can escape the influence of a great and far-reaching idea.
[70] At first sight an apparent contradiction arises from the admission of both heredity and adaptation; and it is undoubtedly true that a strong disposition to heredity precludes great capability of adaptation. But imagine the organism to be a plastic mass which retains the form transmitted to it by former influences until new influences modify it; the one property of plasticity will then represent capability of adaptation as well as power of heredity. Analogous to this is the case of a bar of magnetised steel of high coercive force: the steel retains its magnetic properties until a new force displaces them. Take also a body in motion: the body retains the velocity acquired in (inherited from) the interval of time just preceding, except it be changed in the next moment by an accelerating force. In the case of the body in motion the change of velocity (Abänderung) was looked upon as a matter of course, while the discovery of the principle of inertia (or persistence) created surprise; in Darwin's case, on the contrary, heredity (or persistence) was taken for granted, while the principle of variation (Abänderung) appeared novel.
Fully adequate views are, of course, to be reached only by a study of the original facts emphasised by Darwin, and not by these analogies. The example referring to motion, if I am not mistaken, I first heard, in conversation, from my friend J. Popper, Esq., of Vienna.
Many inquirers look upon the stability of the species as something settled, and oppose to it the Darwinian theory. But the stability of the species is itself a "theory." The essential modifications which Darwin's views also are undergoing will be seen from the works of Wallace [and Weismann], but more especially from a book of W. H. Rolph, Biologische Probleme, Leipsic, 1882. Unfortunately, this last talented investigator is no longer numbered among the living.
[71] Written in 1883.