It is not only a right, but a duty to examine these theories, since they are held seriously and urged earnestly by able men. But we must doubt whether they ought to claim the authority of science. They are proposed by scientific men, and they refer to scientific subjects. But these theories, in their present development, belong to metaphysics rather than to science. Science consists, first, of observation of facts; secondly, of laws inferred from those facts; and thirdly, of a verification of those laws by new observation and experiment. That which cannot be verified is no part of science; astronomy is a science, since every eclipse and occultation verifies its laws; geology is a science, since every new observation of the strata and their contents accords with the established part of the system; chemistry is a science for the same reason. But Darwin's theory of the transformation of species by natural selection is as yet unverified. "There is no evidence of a direct descent of earlier from later species in the geological succession of animals." So says Agassiz, and on this point his testimony can hardly be impeached. Professor W. Thompson, another good geological authority, says: "In successive geological formations, although new species are constantly appearing, and there is abundant evidence of progressive change, no single case has yet been observed of one species passing through a series of inappreciable modifications into another." Neither has any such change taken place within historic times, for the animals and plants found in the tombs of Egypt are "identical, in all respects," says M. Quatrefages, "with those now existing." He adds the opinion, after a very careful and candid examination of the hypothesis of Darwin, that "the theory and the facts do not agree." Not being verified, then, this theory is not yet science, but an unverified mental hypothesis, that is, metaphysics.