The speaker is likely William Holman Hunt (or Holman-Hunt), a British painter and one of the founders of the Pre-Raphaelite Brotherhood. He explains that, during seances, specific persons will come to communicate, but it isn't possible to "call up the dead." They are not as available as people might believe they are. There is also the possibility that a medium may be hearing from a lower-level entity on the other side impersonating the person the sitters want to come through.
43 minutes, recorded 1962