That is an assertion which might reasonably be made: it is not the only way of regarding the matter, however, and the mode in which a magnetic field originates round the path of a moving charge—being generated during the acceleration-period by a pulse of radiation which travels with the speed of light, being maintained during the steady-motion period by a sort of inertia as if in accordance with the first law of motion, and being destroyed only by a return pulse of re-radiation during a retardation-period when the moving charge is stopped or diverted or reversed—all this can hardly be fully explained until the intimate nature of an electric charge has been more fully worked out; and the subject now trenches too nearly on the more advanced parts of Physics to be useful any longer as an analogue for general readers. Indeed it must be recollected that no analogy will bear pressing too far. All that we are concerned to show is that known magnetic behaviour exhibits a very fair analogy to some aspects of that still more mysterious entity which we call "life"; and if anyone should assert that all magnetism was pre-existent in some ethereal condition, that it would never go out of essential existence, but that it could be brought into relation with the world of matter by certain acts,—that while there it could operate in a certain way, controlling the motion of bodies, interacting with forms of energy, producing sundry effects for a time, and then disappearing from our ken to the immaterial region whence it came,—he would be saying what no physicist would think it worth while to object to, what many indeed might agree with. Well, that is the kind of assertion which I want to make, as a working hypothesis, concerning life. An acorn has in itself the potentiality not of one oak-tree alone, but of a forest of oak-trees, to the thousandth generation, and indeed of oak-trees without end. There is no sort of law of "conservation" here. It is not as if something were passed on from one thing to another. It is not analogous to energy at all, it is analogous to the magnetism which can be excited by any given magnet: the required energy, in both cases, being extraneously supplied, and only transmuted into the appropriate form by the guiding principle which controls the operation. We do not know how to generate life without the action of antecedent life at present, though that may be a discovery lying ready for us in the future; but even if we did, it would still be true (as I think) that the life was in some sense pre-existent, that it was not really created _de novo_, that it was brought into actual practical every-day existence doubtless, but that it had pre-existed in some sense too: being called out, as it were, from some great reservoir or storehouse of vitality, to which, when its earthly career is ended, it will return.