Arthur Conan Doyle and Fulton Oursler.

Ad for Fulton Oursler's Behold This Dreamer (1924)
Note blurb from Conan Doyle

This Forbes article on "Imponderable"—a new exhibition of work by artist Tony Oursler at LUMA Westbau (Zurich)—notes one source: a debate on spiritualism between Oursler's grandfather, Charles Fulton Oursler (Reader's Digest editor, author of The Greatest Story Ever Told, and mystery writer Anthony Abbot, 1893–1952), and fellow writer Arthur Conan Doyle.