hand, when the "Old Ones" (fairies) still manifest themselves in England in Keith Roberts's Pavane, which takes place in a technologically backward world after a Spanish assassination of Elizabeth I allowed the Spanish Armada to conquer England, the possibility that the fairies were real but retreated from modern advances makes the POD possible: the fairies really were present all along, in a secret history. Again, in the English Renaissance fantasy Armor of Light by Melissa Scott and Lisa A. Barnett, the magic used in the book, by Dr. John Dee and others, actually was practiced in the Renaissance; positing a secret history of effective magic makes this an alternate history with a point of departure. Sir Philip Sidney survives the Battle of Zutphen in 1586, and shortly thereafter saving the life of Christopher Marlowe. When the magical version of our world's history is set in contemporary times, the distinction becomes clear between alternate history on the one hand and contemporary fantasy, using in effect a form of secret history (as when Josepha Sherman's Son of Darkness has an elf living in New York City, in disguise) on the other. In works such as Robert A. Heinlein's Magic, Incorporated where a construction company can use magic to rig up stands at a sporting event and Poul Anderson's Operation Chaos and its sequel Operation Luna, where djinns are serious weapons of war—with atomic bombs—the use of magic throughout the United States and other modern countries makes it clear that this is not secret history—although references in Operation Chaos to degaussing the effects of cold iron make it possible that it is the result of a POD. The sequel clarifies this as the result of a collaboration of Einstein and Planck in 1901, resulting in the theory of "rhea tics". Henry Moseley applies this theory to "degauss the effects of cold iron and release the goetic forces." This results in the suppression of ferromagnetism and the re-emergence of magic and magical creatures. Alternate history shades off into other fantasy subgenres when the use of actual, though altered, history and geography decreases, although a culture may still be clearly the original source; Barry Hughart's Bridge of Birds and its sequels take place in a fantasy world, albeit one clearly based on China, and with allusions to actual Chinese history, such as the Empress Wu. Richard Garfinkle's Celestial Matters incorporates ancient Chinese physics and Greek