Painting in Düsseldorf at the time when Wilhelm Schadow was director of the art academy was of world rank. Not a few considered what was happening artistically in Düsseldorf to be as important, perhaps even more important, than what was happening in Berlin, in Munich, in Paris. This was not in spite of, but because of the pictorial strategy characteristic of the "Düsseldorf School of Painting" of translating poetry into painting, of making reflections and feelings -- i.e. the invisible -- the subject. The invis- ible, which only appears before our inner eye, does not make the paintings poorer. On the contrary, it makes them richer. The paintings of the Düsseldorf School of Painting attracted particular criticism for their depiction of the non-representable. What the invisible of painting can be, and how it manifested itself in the perception of contemporaries, is the subject of this book.