Are “stern” and “just” adjectives for “spirit”? Does “spirit” refer to a supernatural being?

Question

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)}

Answer 1

no, "spirit" here refers to the attitude of the inquiry

Answer 2

"Spirit",like many English words, has more than one definition. It can mean an incorporeal, supernatural being. But it can also mean an attitude or personal quality. Like you might say, "John had a very determined spirit" or "The team had a fighting spirit" or "She was depressed and her spirit was very low".

Here it means the second. It is referring to the attitude of Mr Crookes, or more specifically, the attitude with which he pursued his inquiries. In general, saying, "Mr Jones has an X spirit" is the same as saying "Mr Jones is X", where "X" is some sort of personality trait or attitude. Like here, saying "Mr Crookes had a stern and just spirit" is essentially the same as saying "Mr Crookes was stern and just", just a little more poetic.

It's a little ironic that the writer used the word "spirit" in this non-supernatural sense in a paragraph talking about the supernatural. I don't know if that was a deliberate play on words or unintentional.