Smith with his friend William Crookes, attended a séance on 21 April 1870 in London. He sent Crookes 15 letters on spiritualism between April 1869 and 1871. Smith did not choose to write widely about spiritualism as he believed it might damage his scientific reputation. He was a member of the Society for Psychical Research from 1882 to 1884. After he died, 89 books on the occult were discovered in his library.