It must not be imagined, finally, that the summoning of spirits is a lost art; even in our day men are found who are willing to call the departed from their resting-place, and to exhibit them to the eyes of living men. The best explanation of this branch of magic was once given by a learned professor, whom the Prince Elector of Brandenburg, Frederick II., sent for from Halle, in order to learn from him how spirits could be summoned. The savant declared that nothing was easier, and supported his assertion by a number of actual performances. First the spectator was prepared by strong beverages, such as the Egyptian sorcerers already used to employ on similar occasions, and by the burning of incense. Soon he fell into a kind of half-sleep, in which he could still understand what was said, but no longer reflect upon the sense of the words; gradually his brain became so disturbed, and his imagination so highly excited, that he pictured to himself images corresponding to the words which he heard, and called them up before his mind's eye as realities. The magician, protected against the effects of the incense by a sponge filled with an alcoholic mixture, then began to converse with his visitor, and tried to learn from him all he could concerning the person the latter wished to see, his shape, his clothes, etc. Finally the victim was conducted into a dark room, where he was suddenly asked by a stern, imperious voice: "Do you not see that woman in white?" (or whatever the person might be,) and at once his over-excited imagination led him to think that he really beheld what he expected or wished to see. This was allowed to go on till he sank down exhausted, or actually fainted away. When he recovered his consciousness, he naturally recollected but imperfectly what he had seen while in a state of great excitement, and his memory, impaired by the intermediate utter exhaustion and fainting, failed to recall the small errors or minute inaccuracies of his vision. All that was left of the whole proceeding was a terrifying impression on his mind that he had really seen the spirits of departed friends.