Baarn, the artist, 1952. Four prints (paper size 17.5 x 15.5 cm each; print size 16.0 x 13.5 cm each), each printed in three colours. Additional text printed on versos.

A complete set of four designs, commissioned by the engineer Eugène Strens and his wife, Willy Strens. Each print monogrammed "MCE" in the figure. The four illustrations represent the classical four elements, as follows: Aarde [Earth], titled: Eugène & Willy Strens / Felicitas 1953; Lucht [Air], titled: Felicitas 1954 / Eugène & Willy Strens; Vuur [Fire] titled: Eugène & Willy Strens / Felicitas 1955; and Water, titled: Felicitas 1954 / Eugène & Willy Strens. The printing colours are dark blue and brown (Earth), green and red (Air), red and orange (Fire), and green and blue (Water). The titles are printed in grey, as is the text in the verso's margin, stating, implicitly, copyright, title, and number within the series of four, as well as another, unexplained number. Escher explained the four different mathematical design structures to Strens: "The system of Fire is based solely on glide reflection; in Water, a rotation around a twofold axis, located in the centre of the square, occurs, i.e., all the blue fish are congruent 'en bloc' with the brown [fish]; Air is a shifting system, in which neither axes nor reflection occurs. ... Earth ... is based on another system: in it, there are twofold and fourfold axes." Provenance: three prints with an address stamp of Eugène Strens on verso; otherwise, unmarked. Some very light creasing, a few insignificant smudges on verso, otherwise, near fine. Bool 382, 383, 384, and 385.