I actually find this part of the story one of the more amusing sections. It comes towards the beginning, after Dr. Heidegger has announced his intention of performing an experiment with the help of his guests. They, obviously knowing the doctor of old, expect something mundane and boring:
When the doctor's four guests heard him talk of his proposed experiment, they anticipated nothing more wonderful than the murder of a mouse in an air pump, or the examination of a cobweb by the microscope, or some similar nonsense, with which he was constantly in the habit of pestering his intimates.
However, instead of any of these possibilities, Dr. Heidegger brings his folio, bound in black leather, to the table. Note how "common report" affirmed this folio to be a "book of magic," which seems to foreshadow the supernatural and miraculous nature of the experiment that we, just like Dr. Heidegger's guests, are about to witness.