When Wells' Time Traveller first glimpses Morlocks as white figures at night, he remembers Grant Allen's notion that, if each generation dies and leaves ghosts, then the world should eventually become overcrowded with such ghosts. In The Goblin Reservation by Clifford Simak, because a future University has both a Time Travel Department and a Supernatural Department, William Shakespeare is able to meet his own ghost. See here.
This idea of ghosts in the future has enabled us to assemble references to:
Names to conjure with. I had never heard of Grant Allen before but he is yet another period reference in The Time Machine. It is late, approaching the hour at which people see ghosts, and I am out of here.