Johannes Geller, index of the collection of the lawyer Johannes Geller in Neuss, n. p. [printed in Munich], 1943, no. 26; Peg DeLamater, Klee and India: Krishna Themes in the Art of Paul Klee, Diss. University of Texas, Austin 1991, p. 217; Christian Rümelin, Klee's handling of his own oeuvre, in: Paul Klee, Years of Mastery 1917-1933, exhib. cat. Stadthalle Balingen 2001, p. 21-37 and 215-222, p. 219 annot. 69; Max Tauch, The Society for the Promotion of German 20th Century Art and Paul Klee, in: Paul Klee in the Rhineland. Drawings, watercolours, gouaches, exhib. cat. Art and Exhibition Hall of the Federal Republic of Germany, Bonn 2003, p. 45-52, p. 50-52; Michael Baumgartner, "a very special spectacle, the crowd and the incredible boldness on the high wire". Paul Klee's fascination with the circus and acrobats, in: Paul Klee. Theater everywhere, exhib. cat. Zentrum Paul Klee, Bern 2007, p. 227-233, p. 229