But they applied this knowledge, which must have been gathered from long observations, mainly to practical purposes, such as the reform of the calendar and the orientation of the pyramids, temples, and tombs, rather than to mythology. The idea of a future life, which took such a firm hold of all classes of ancient Egypt, is that to which we are indebted for the preservation of these wonderful records of the remote past. The theory was that man consisted of three parts; the body or ordinary living man; the Ka or Double, which was a sort of shadowy self which came out of the body and returned to it as in dreams; and the soul, a still more subtle essence, which at death went to the gods, was judged, and either rewarded for its merits by living with them in heaven, or punished for its sins by being sent to the nether world of torment. But this soul still retained such a connection with its former body as to come down from time to time to visit it; while the Ka or Double retained the old connection so closely as to live habitually in it, only coming out to eat, drink, and repeat the acts of its former life, but incapable of existing without a physical basis in the old body or some likeness of it. The same doctrine of the Double was applied to all animated and even to inanimate objects, so that the shadowy man could come out of his mummy, live in his own shadowy house, feed on shadowy food, be surrounded by shadowy geese, oxen, and other objects of his former possessions. Hence arose the extraordinary care in providing a fitting tomb and preserving the mummy, or, failing the mummy, which in course of time might decay, providing a portrait-statue or painted likeness, which might give a _point d'appui_ for the Ka, and a receptacle for the occasional visits of the soul. While these were preserved, conscious personal life was continued beyond the grave, and the good man who went to heaven was immortal. But if these were destroyed and the physical basis perished, the Ka and soul were left without a home, and either perished also, or were left to flit like gibbering ghosts through the world of shadows without a local habitation or a name. The origin of this theory as regards the Ka is easily explained. It is, as Herbert Spencer has conclusively shown, a natural inference from dreams, and is found everywhere, from interments of the stone period down to the crude beliefs of existing savages. It even survives among many civilized races in the belief in ghosts, and the precautions taken to prevent the Ka's of dead men from returning to haunt their former homes and annoy their posterity. The origin of the third element or soul is not so clear. It may either be a relic of the animism, which among savage races attributes life to every object in nature, or a philosophical deduction of more advanced periods, which sees an universal spirit underlying all creation, and recognizing in man a spark of this spirit which is