Madame Helena (HP) Blavatsky briefly lived at the Hotel St George in 1874, a year before starting up her Theosophical Society in New York. At this point in her life she had become obsessed with the idea of the Emerald Tablet of Hermes and the alchemical learnings of John Dee and Giordano Bruno. Still fourteen years away from publishing her magnum opus The Secret Doctrine, Blavatsky was looking for a quiet place to perform some experiments, and the Hotel St George - never a place to balk at such requests from its patrons - was more than happy to provide her with a room.
While stories differ as to the various sounds and emanations which came from what was then called "Helena's Lab," the common consensus was that they were unearthly and mildly disturbing. Blavatsky wished to be left alone, and with a certain exchange of currency, her wishes were fully respected. The only others besides HP who were ever seen entering and leaving the room were a few dubious looking characters, heavily robed, and clearly of foreign extraction.
When the Theosophical Center was finally ready, Blavatsky quietly packed her things up and left. Initial exploration of the laboratory was a bit of a let down. It appeared to have been completely emptied out, much to the chagrin of the management, but to the happiness of the cleaning staff. The only remnants of Madame having ever been there were words burned in a delicate hand on the wooden floor in a far corner of the room reading, "As above, so below."
Madame Blavatsky never forgot the kindness and discreteness of the Hotel. Many years later, after the success of The Secret Doctrine, she donated an undisclosed amount to the Hotel St George. A plaque was installed in the Laboratory as a reminder of her kindness, curiosity and generosity. Her one request was to name the room the "Henderson Laboratory;" whom or what Henderson was, she never revealed. Perhaps one of the strangers seen leaving the lab on a rainy night, perhaps one of the spirits she summoned within its walls, perhaps a pet loved long ago.
The Henderson Laboratory is still used as a research center of sorts, where patrons can explore and craft ideas of there own. The use of the lab is free, provided the standard application and proposal procedure has been followed.