Of course, this isn't Bessie's first time being floated. While touring Canada early in their careers, the Houdinis performed a version of the Trilby levitation.
The irony of this photo is that Blackstone was a rival to Houdini. The men clashed several times. Once when Blackstone floated a large balloon advertising his show near a theater where Houdini was playing, Houdini considered shooting it down, but feared that would just draw more attention to it. He even filed a complaint with the National Variety Artists to stop Blackstone from performing his overboard box escape. In return, Blackstone frequently took swipes at Houdini's ego. In Milbourne Christopher's Panorama of Magic (1962), the author recalls:
The first time Blackstone visited my apartment he went from room to room, stopping now and again to examine a print, a painting or a book more closely. Finally, as he came to the colorful lithographs, he said: "Houdini used to have a place like this. The only difference is that all of his pictures were of Houdini."
After the deaths of Houdini and Thurston, Blackstone became the preeminent magician of his day, and really the last great stage magician of the Golden Age of Magic. He died in 1965 at age 80 in an apartment just blocks from The Magic Castle in Hollywood.
For more on the career of Harry Blackstone, check out the first part of an excellent profile by Michael Lauck over at iTricks: Blackstone: The Last Great Stage Show.