Definition of "mercurism"

Altho at this distance you had no early Account or Particular of his Death; yet your Affection may cease to wonder that you had not some secret Sense or Intimation thereof by Dreams, thoughtful Whisperings, Mercurisms, Airy Nuncio's, or sympathetical Insinuations, which many seem to have had at the Death of their dearest Friends:

1690, Sir Thomas Browne, A Letter to a Friend