Moreover—and why not proclaim it loudly—all that science of which we are so proud, is only knowledge of appearances. The real nature of things baffles us. The innermost nature of laws governing matter, whether living or inert, is inaccessible to our intelligence. A stone tossed up into the air falls back again to the earth. Why? Newton says through attraction proportional to bulk and distance. But this law is only the statement of a fact; who understands that attractive vibration, which makes the stone fall? The fall of a stone is such a commonplace phenomenon, that it does not astonish us: but in reality no human intelligence has ever understood it. It is usual, common, accepted; but like all Nature’s phenomena without exception it is _not understood_. After fecundation an egg becomes an embryon; we describe as well as we can the phases of this phenomenon; but, in spite of the most minute descriptions, have we understood the evolution of that cellular protoplasm, which is transformed into a huge, living being? What prodigy is at work in these segmentations? Why do these granulations crowd together there? Why do they decay here to form again elsewhere? We live in the midst of phenomena and have no adequate knowledge of any one of them. Even the simplest phenomenon is most mysterious. What does the combination of hydrogen with oxygen mean? Who has even once been thoroughly able to understand that word _combination_, annihilation of the properties of two bodies by the creation of a third body differing from the two first. How are we to understand that an atom is indivisible; it is constituted of a particle of matter, yet—even in thought—it cannot be divided! Therefore it behoves the true savant to be very modest, yet very bold at the same time: very modest, for our science is a mere trifle—Ἡ ἀνθρωπίνη σοφία ὀλίγου τινος ἄξιά ἐστι, καί οὐδενός—very bold, for the vast regions of worlds unknown lie open before him. Audacity and prudence: such are the two qualities, in no wise contradictory, of Dr. Maxwell’s book. Whatever be the fate in store for his ideas—ideas based upon facts—we may rest assured that the facts, which he has well observed, will remain. I think I see here the lineaments of a new science—though only a crude sketch so far. Who knows but that physiology and physics may find herein some precious elements of knowledge? Woe to the savants who think that the book of Nature is closed, and that we puny men have nothing more to learn. CHARLES RICHET. CONTENTS PAGE INTRODUCTION BY SIR OLIVER LODGE, v PREFACE BY PROFESSOR CHARLES RICHET, xv PRELIMINARY REMARKS, 1