The literal meaning is a neat, orderly person, but I am inclined to think that the meaning is more in the sense suggested in a famous quote by Mark Twain which says:
- Be careless in your dress if you will, but keep a tidy soul
- Twain is telling us that it doesn’t matter what we look like on the outside. We can dress however we want, we don’t need to be concerned with our image, as long as our souls are ‘tidy.’ To keep a tidy soul is to live as a good person; to refrain from doing things which you know are wrong or evil. If you keep a tidy soul, then people will not judge you by the way you dress, but by the way you live your life.
Mr. Christian Friedrich Schönbein is described as a nice and correct person.