Are "stern" and "just" adjectives for "spirit"? Does "spirit" refer to a supernatural being?
The research into the phenomena of Spiritualism by Sir William Crookes —or Professor Crookes, as he then was—during the years from 1870 to 1874 is one of the outstanding incidents in the history of the movement. It is notable on account of the high scientific standing of the inquirer, the stern and yet just spirit in which the inquiry was conducted, the extraordinary results, and the uncompromising declaration of faith which followed them.
The History of Spiritualism By A.C Doyle
XI.THE RESEARCHES OF SIR WILLIAM CROOKES (1870-1874)