An English naturalist, Mr. Darwin, has shown that in the successive life of animal generations, the favorable variations which are produced in the organization of a being are transmitted to its descendants and insure the perpetuity of its race, while the unpropitious variations disappear because they entail the destruction of the races in which they are produced. He tells us: "This preservation of favorable variations and the rejection of injurious variations, I call Natural Selection."[114] What does the author understand by law? He answers: "the series of facts as it is known to us."[115] Here we have the true definition of law: it is the simple expression of the series of the facts; the cause remains to be sought for. I open the book in another part. The author is speaking of the eye; and his doctrine is that the eye of the eagle was formed by the slow transformations of an extremely simple visual apparatus. There will have been then, in the development of animal existence, first of all a rudimentary eye, then an eye moderately well formed, and then the eye of the eagle, because the favorable modifications of the organ of sight will have been preserved and increased in the course of ages. Such is the series of facts, such is the law; suppose we grant it. What is the cause? The optician makes our spectacles; who made the eye of the eagle, by directing the slow transformations which at length produced it? Let us listen to the author: "There exists an intelligent power, and that intelligent power is natural selection, constantly on the watch for every alteration accidentally produced in the transparent layers, in order carefully to choose such of those alterations as may tend to produce a more distinct image.... Natural selection will choose with infallible skill each new improvement effected."[116] Natural selection is a law; a law is the series of facts; it seems that we must seek for the power which directs this series of facts; but, lo, the series of facts itself is transformed into a power--into an intelligent power--into a power which chooses with infallible skill! The confusion of ideas is complete. The mind is on a wrong scent; it concludes that the law explains everything, and has itself no need of explanation. The idea of the cause disappears, and, as Auguste Comte expresses it, "science conducts God with honor to its frontiers, thanking Him for His provisional services."[117] This is not perhaps the idea of Mr. Darwin, but it is at any rate the idea of some of his disciples, as we shall see by-and-by.