The mazurka movement and the augmented fourth degree of the scale (Nos.

Tritone, augmented fourth, known as "the devil in musick" from early medieval times.

The melodic progression, not always immediate, of an augmented fourth and major seventh occurs frequently, and that of an augmented second occasionally.

The oriental interval of the augmented fourth, which I scent in the "Mondlied," would be written, I think, more simply thus:-