Page:Popular Science Monthly Volume 2.djvu/127

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empty a priori speculations which have figured so largely in the past career of the human mind. It is the result of the steady concentration of the intellect of man for hundreds of years upon the realities that surround us, and is the profoundest answer yet given to man's questionings of the mystery of being. It is the latest interpretation of the ongoings of the world, and brings with it the possibility of a new and more stable philosophy of things than we have yet known—a philosophy not spun from mystical a priori fancies, but constructed from the valid truths of science, and anchored in the depths of demonstrated knowledge.

An able writer in the Quarterly Review (London) for July, in discussing the modern school of thought and Herbert Spencer's relation to it, says: "The two deepest scientific principles now known of all those relating to material things are, the law of gravitation and the law of evolution." The principle is here recognized as more than a hypothesis and more even than a theory, it is a law in the same sense that gravitation is a law. The proof of evolution indeed is very far from being so complete as that of gravitation. But its claims as an established law are not therefore invalidated, for the accepted truths of science by no means rest upon equal amounts of evidence. From the newness of the systematic investigation of the principle, from the imperfection of knowledge in many spheres of its application, and from the stupendous reach of its operation, it is impossible that there should not be many deficiencies in its proof. It has its outstanding and unresolved difficulties which it may take long to clear up. Truths grow—they are examples of evolution. All great generalizations have been arrived at gradually; never at once by complete demonstration. There are first long foreshadowing preludes in which a principle is discerned as emerging into increasing distinctness. It is then accepted on grounds of probability, and preponderating proofs, and as an advance on previous beliefs. If a theory becomes increasingly consonant with facts, and steadily makes way against inexorable criticism, though it has grave difficulties, it will be accepted, and these difficulties will be left to the future. It was so with the law of gravitation. "The Newtonian theory was beset by palpable contradictions in its results till many years after Newton's death, yet all sound philosophers embraced it. The motion of the apsides of the moon's orbit was with singular honesty confessed by Newton to be, in fact, nearly twice as great as calculation from theory made it; and this contradiction remained an outstanding, palpable objection, yet without occasioning any misgiving as to the general truth of gravitation, until the error was explained and the calculation rectified by Clairault."

And so it is in other branches of science. The undulating theory of light is accepted by all physicists, but still has its difficulties. The theory of heat is not without its anomalies. The chemical theory of respiration is generally adopted, but there are facts that still oppose it. It is claimed by none, that the evidence of the law of evolution is complete, but it is a growing conviction of those who know the subject best, that the evidence in its favor preponderates overwhelmingly. Nor is it dependent upon any of its special interpretations. Darwin may be in error, Huxley may be wrong, Mivart may be wide of the mark, Haeckel may be mistaken, Cope may misjudge, and Spencer be at fault; but, in common with a large and increasing body of scientific men, they are all agreed as to one thing, that evolution is a great and established fact—a wide and valid induction from the observed order of Nature, the complete elucidation of which is the grand scientific task of the