ing a picture of the reality? To such a question I might reply, "Thou shalt not make unto thee any image or any likeness!" Our object is not to see the world in a more or less darkened or distorted glass, but as immediately as the constitution of our mind will permit. To set realities, demonstrable and measurable magnitudes, in definite relations with one another, so that when one is given the others will follow—that is the purpose of science, and it can not be fulfilled by the substitution of any hypothetical figure, but only by the demonstration of the mutual dependencies of measurable magnitudes.
This road is undoubtedly long and toilsome, but it is the only permissible one. We do not have to go upon it, however, despairing of ourselves seeing the end of it, and merely hoping that it may lead our children to the desired heights. No, we ourselves are the happy ones, and the most hopeful scientific gift which the departing century can offer the dawning one is the replacement of the mechanical theory by the energistic.
I lay at this point great weight on the declaration which I make that we are not dealing with some fresh novelty, first given in our time. No, we have been in possession of the truth for half a century without knowing it. If there ever was a place for the expression "mysteriously evident," it is here; we can read it every day, and do not understand it.
When fifty-three years ago Julius Robert Mayer first discovered the equivalence of the different natural forces, or, as we should say now, of the various forms of energy, he made a great advance toward an ultimate solution of the problem. But, according to a constantly recurring law in universal thought, a new fact is never accepted in its primary clearness and simplicity. The receiver, who has not inwardly felt the advance, but has taken it in from without, strives first of all things to connect the new as well as he can with what is already existing. Hence the new thought is obscured, and, although not exactly falsified, is robbed of the best of its force. So strong is this peculiarity of thought that it does not even leave the discoverer free; as even the powerful mind of Copernicus was competent to let the sun and earth change places in their motions, but not to comprehend the simple motions of the other planets; to account for these he adhered to the received theory of epicycles. So it was with Mayer. Hence, as it nearly always is, the work of the next generation consists, not in harvesting the results of the new knowledge, but rather in removing again, piece by piece, the involuntary additions that do not belong to the subject, till at last the fundamental thought can come out in its whole plain identity.
A similar development can be perceived, even in our case. After J. R. Mayer had-defined the law of equivalence, his theory
