Among Klee's particular achievements during the war and postwar years was his attempt to bring his art closer to music—a task he had been working on since the beginning of the century. "Rhythm of Windows and Firs" from 1919 is among the first works in which he experimented with a connection between musical and visual composition, before he systematically employed musical notation as a matrix in his "rhythmic landscapes" the following year. The painting's title itself alludes to music, a connection reinforced by the unusual design of the reverse side. There, Klee had covered the cardboard and frame with sheet music from the psalms of the Regensburg composer Franz Xaver Engelhart (1861–1924), thus adding a hidden message to the painting. Whether he intended to establish a direct link between the painting and these specific compositions remains unclear. However, it does contain a programmatic reference to the analogy between musical notation and pictorial notation, between the rhythm of the tones and that of the squares and rectangles on the picture plane.