Let me illustrate this conception by a return to the metaphor of the "conscious spectrum" to which I introduced my reader in the first chapter. I there described our conscious spectrum as representing but a small fraction of the _aurai simplicis ignis_, or individual psychical ray;--just as our visible solar spectrum represents but a small fraction of the solar ray. And even as many waves of ether lie beyond the red end, and many beyond the violet end, of that visible spectrum, so have I urged that much of unrecognised or subliminal faculty lies beyond the red (or organic) end, and much beyond the violet (or intellectual) end of my imaginary spectrum. My main task in this book will be to prolong the psychical spectrum beyond either limit, by collecting traces of latent faculties, organic or transcendental:--just as by the bolometer, by fluorescence, by other artifices, physicists have prolonged the solar spectrum far beyond either limit of ordinary visibility. But at present, and before entering on that task of rendering manifest supernormal faculty, I am considering what we ought to regard as the normal range of faculty from which we start;--what, in relation to man, the words _norm_ and _normal_ should most reasonably mean. The word _normal_ in common speech is used almost indifferently to imply either of two things, which may be very different from each other--conformity to a standard and position as an average between extremes. Often indeed the average constitutes the standard--as when a gas is of normal density; or is practically equivalent to the standard--as when a sovereign is of normal weight. But when we come to living organisms a new factor is introduced. Life is change; each living organism changes; each generation differs from its predecessor. To assign a fixed norm to a changing species is to shoot point-blank at a flying bird. The actual average at any given moment is no ideal standard; rather, the furthest evolutionary stage now reached is tending, given stability in the environment, to become the average of the future. Human evolution is not so simple or so conspicuous a thing as the evolution of the pouter pigeon. But it would be rash to affirm that it is not even swifter than any variation among domesticated animals. Not a hundred generations separate us from the dawn of history;--about as many generations as some microbes can traverse in a month;--about as many as separate the modern Derby-winner from the war-horse of Gustavus Adolphus. Man's change has been less than the horse's change in physical contour,--probably only because man has not been specially bred with that view;--but taking as a test the power of self-adaptation to environment, man has traversed in these thirty centuries a wider arc of evolution than separates the racehorse from the eohippus. Or if we go back further, and to the primal germ, we see that man's ancestors must have varied faster than any animal's, since they