But besides the doctrine of metempsychosis, which proved such a fertile mother of fable, there was another article of popular mythology which gave rise to stories of transformation. Among the abundant superstitions existing relative to transformation, three shapes seem to have been pre-eminently affected—that of the swan, that of the wolf, and that of the serpent. In many of the stories of those transformed, it is evident that the individual who changes shape is regarded with superstitious reverence, as a being of a higher order—of a divine nature. In Christian countries, everything relating to heathen mythology was regarded with a suspicious eye by the clergy, and any miraculous powers not sanctioned by the church were attributed to the evil one. The heathen gods became devils, and the marvels related of them were supposed to be effected by diabolic agency. A case of transformation which had shown the power of an ancient god, was in Christian times considered as an instance of witchcraft. Thus stories of transformation fell into bad odour, and those who changed shapes were no longer regarded as heavenly beings, commanding reverence, but as miserable witches deserving the stake. In the infancy of the world, when natural phenomena were ill-understood, expressions which to us are poetical were of a real significance. When we speak of thunder rolling, we use an expression which conveys no further idea than a certain likeness observed between the detonations and the roll of a vehicle; but to the uninstructed mind it was more. The primæval savage knew not what caused thunder, and tracing the resemblance between it and the sound of wheels, he at once concluded that the chariot of the gods was going abroad, or that the celestial spirits were enjoying a game of bowls. We speak of fleecy clouds, because they appear to us soft and light as wool, but the first men tracing the same resemblance, believed the light vapours to be flocks of heavenly sheep. Or we say that the clouds are flying: the savage used the same expression, as he looked up at the mackerel sky, and saw in it flights of swans coursing over the heavenly lake. Once more, we creep nearer to the winter fire, shivering at the wind, which we remark is howling around the house, and yet we do not suppose that the wind has a voice. The wild primæval men thought that it had, and because dogs and wolves howl, and the wind howled, and because they had seen dogs and wolves, they concluded that the storm-wind was a night-hound, or a monstrous wolf, racing over the country in the darkness of the winter night, ravening for prey.