In 1854, Dr. Luther V. Bell, director of the McLean Asylum for the Insane in Boston, scientifically tested the capabilities and veracity of several psychic mediums.
During his studies, he claimed to have seen both the realization of extraordinary mental gifts as well as the manifestation of measurable physical phenomena as well. For instance, during one test, a table was witnessed to have moved twice from one room to another. Another medium was able to contact Bell's brother who had died 25 years before.
While the communication was startling detailed, eschewing most all doubts, Bell was still troubled by something. Through further experimentation, Bell came to believe that the medium wasn't in contact with the spirit of any dead brother. Rather, the medium only knew what Bell himself knew; if he were ignorant of the answer to any question posed, the medium (or the "spirit" of Bell's brother) would be equally ignorant--even when he should have known the response.
This all led Bell to conclude that while the psychic gift was real, it didn't extend to the spirit realm. Still, this was a remarkable confirmation in and of itself.