_Mobility and Mutability of the Sidereal World._—This is not true, in the first place, of the sidereal bodies. The ancients held the sidereal world to be immutable and incorruptible. The doctrine of the incorruptibility of the heavens prevailed up to the seventeenth century. The observers who at that epoch directed towards the heavens the first telescope, which Galileo had just invented, were struck with astonishment at discovering a change in that celestial firmament which they had hitherto believed incorruptible, and at perceiving a new star that appeared in the constellation Ophiuchus. Such changes no longer surprise us. The cosmogonic system of Laplace has become familiar to all cultivated minds, and every one is accustomed to the idea of the continual mobility and evolution of the celestial world. “The stars have not always existed,” writes M. Faye; “they have had a period of formation; they will likewise have a period of decline, followed by final extinction.” Thus all the bodies of inanimate nature are not eternal and immutable; the celestial bodies are eminently susceptible of evolution, slow indeed with that we observe on the surface of our globe; but this disproportion, corresponding to the immensity of time and of cosmic spaces as compared with terrestrial measurements, should not mislead us as to the fundamental analogy of the phenomena. § 1. THE MOVEMENT OF PARTICLES AND MOLECULES IN BRUTE BODIES. It is not only in celestial spaces that we must search for that mobility of brute matter which imitates the mobility of living matter. In order to find it we have only to look about us, or to inquire from physicists and chemists. As far as geologists are concerned, M. le Dantec tells us somewhere of one who divided minerals into _living rocks_—rocks capable of change of structure, of evolution under the influence of atmospheric causes; and _dead rocks_—rocks which, like clay, have found at the end of all their changes a final state of repose. Jerome Cardan, a celebrated scientist of the sixteenth century, at once mathematician, naturalist, and physician, declared not only that stones live, but that they suffer from disease, grow old, and die. The jewellers of the present day use similar language of certain precious stones; the torquoise, for example. The alchemists carried these ideas to an extreme. It is not necessary here to recall the past, to evoke the hermetic beliefs and the dreams of the alchemists, who held that the different kinds of matter lived, developed, and were transmuted into each other.