Such a gathering as might raise the spirits? (6)
I believe the answer is:
seance
'such a gathering' is the definition.
(seance is a kind of gathering)
I don't understand the remainder of the clue.
(Other definitions for seance that I've seen before include "Spiritualist meeting, all hold hands" , "Sitting with a medium" , "Spiritualists meeting with medium" , "Spiritualist meeting to contact the dead" , "Psychic gathering" .)