the calculations of Lord Kelvin and others, that a molecule is as small in a drop of water as a marble in comparison with the earth, then we may not look for these creatures. If we can not find them, we do not know that they exist. If we do not know that they exist, shall we "believe" that they do? Is it not better, as Emerson suggests, that we should not "pretend to know and believe what we do not really know and believe"?
It may be that the existence of life in a world once lifeless renders spontaneous generation a "logical necessity." But the "logical necessity" exists in our minds, not in Nature. Science knows no "logical necessity," for the simple reason that we are never able to compass all the possibilities in any given case.
If we are to apply philosophic tests to the theories of reincarnation, we may find them equally eligible as articles of belief. They are plausible, to some minds at least; they have logical continuity. They are satisfying to the human heart, at least this is claimed by their advocates. Their chief fault is that they can be brought to no test of science and have no basis in inductive knowledge. In other words, their only reality is that of the vapors of dreamland. If plausibility and acceptability serve as sufficient foundations for belief, then belief itself is a frail and transient thing, no more worthy of respect than prejudice, from which indeed it could not be distinguished. Some such idea as this seems to be present in the mind of Mr. Gladstone. In a recent article, quoting in part the language of the honest Bishop Butler, he ascribes to certain doctrines "a degree of credibility sufficient for purposes of religion, and even a high degree of probability." In other words, religion, which deals with human hopes and fears, has less need of certainty than science, which is ultimately concerned with human action.
Haeckel makes the same distinction clearly enough. He uses the term "belief" for "hypotheses or conjectures of more or less probability" by which "the gaps empirical investigation must leave in science are filled up. . . . These," he says, "we can not indeed for a time establish on a secure basis, and yet we may make use of them in the way of explaining phenomena, in so far as they are not inconsistent with the rational knowledge of Nature. Such rational hypotheses," he says, "are scientific articles of faith." It is not clear, however, that so large a name as faith need be taken for working hypotheses confessedly uncertain or transient. The word "make-believe," used by Huxley in some such connection, might well be applied to hypothetical "articles of faith," until given a basis by scientific induction. But it seems to me that it is not necessary for the man of science to say "I believe," in addition to "I know." He should put off the livery of science when he enters the service of the Delphian oracles.
