When dust, dirt or other impurities built up in the mercury, part of the light house keeper’s job was to strain the mercury through a fine cloth. … Like the hatters of their day, the light house keepers were being driven mad by exposure to mercury fumes. The solitude was not driving the lighthouse keepers mad.

For many years, lighthouse keepers got their job through political patronage. … But lighthouses often stood on barren ledge far out to sea, and life could get lonely for the keeper and his family. Some lighthouses are said to be haunted by the ghosts of lighthouse keepers driven mad by the monotony and isolation.