After several hours’ drive, they stopped at the marble palace of Potsdam, near the one which the prince was accustomed to occupy. His highness looked cautiously around, and breathed more freely, as he felt that he was now surely among friends. The white palace stood silent and deserted in the darkness, this palace at Potsdam being only used for the guests of the king. The carriage stopped at the side-door, where there was no sentinel, and they alighted, entering the palace, winding along the corridors in the same order as before, guided by the glimmering light of the one preceding. Solemn music, strange ringing sounds, fell upon the ear as they advanced. Sometimes they were sharp and cutting as glass, then threatening and penetrating as the wind, shrieking and moaning, causing one to be very nervous if not terrified. The farther they proceeded the louder grew the sounds, and at intervals groans, moans and wailings were heard, as of those waiting and imploring for mercy. One of the brothers now opened a door, and then placing themselves upon each side, the unknown voice announced to the prince that they had arrived at the long-sought-for goal. “What have we come here for?” asked the prince. “To behold that which you have many times petitioned to be permitted to see,” replied Bischofswerder, gently encouraging and inspiring Frederick William. “The Invisibles have at last yielded to your wishes, and the spirits which you summon will appear. If your courage fails you, and you dread the presence of the departed, command to be reconducted to your palace, and we will obey; but renounce forever the sublime happiness of beholding the Invisibles and of holding communion with the spirit-world!” “I fear not, but wish to be in the company of the spirits,” answered the prince, proudly. “Kneel,” they commanded, permitting him to enter, “and thrice summon in a loud voice the names of three departed, who will answer your questions. Beware of approaching them, for their glance is death and their breath destruction! Therefore remain kneeling, as it becomes a mortal in the presence of an immortal. Hope and pray, brother!” As the door closed upon the prince, and he found himself in such impenetrable darkness, he sank upon his knees, for he dared not advance, and retreat was impossible, in spite of heart-quakings. The shrill, penetrating music ceased, and a voice from a distance called: “Summon thrice those that thou desirest to see.” “Marcus Aurelius, Leibnitz, and the distinguished elector,” called the prince in a loud voice. “Who summoned me?” was responded in hollow, sepulchral tones, and directly over the crown prince a blue, vaporous light was visible--at first only a cloud, then by degrees increasing and condensing itself into a human shape, until it took the form of a Roman warrior of the olden time; no other than Marcus Aurelius, in helmet and coat-of-mail, with a pale, earth-colored face and glaring eyes.