The words εἴδωλον, _simulacrum_, _imago_, especially express the complete resemblance of the dead to the living. Are not the beings who return to talk with us in dreams exactly like the persons we have known? This tenuous image was compared to the reflection seen on limpid waters or on the polished surface of metal.[417] Both alike reproduced the features and colour and imitated the movements of those whom they faithfully expressed. This is why magicians often made use of mirrors in order to evoke the spirits of the departed.[418] As to the nature of these _simulacra_, the ancients agree in declaring them to be material, for how otherwise could they convey sensual impressions? But their substance is of an extreme subtlety. They are forms which are corporeal but empty, flimsy, impalpable, often of such rarity that they remain invisible. They are compared to the wind, for the wind is the air in motion, to a vapour, to a smoke which escapes so soon as its restraint is attempted. This shade, formed of a light fluid, has a form which is necessarily malleable and yielding. The fact is thus explained that souls can take on various appearances and sometimes let themselves be seen as terrible monsters, especially if they are the souls of criminals who have become maleficent spirits.[419] Heroes, on the contrary, whose virtue has enabled them to be borne to heaven, appear to be of more than natural stature when they descend from the ether; they are surrounded by a radiant nimbus, and their resplendent beauty strikes with admiration those who perceive them. But here the ancients were faced with the question as to whether that part of the human composition which won to heaven was the same as that which descended to the infernal regions.