**If a square is added to one of the longer sides of a harmonic rectangle having a side-to-side ratio F, a further harmonic rectangle with size ratio F is obtained. The square is the gnomon of the harmonic rectangle, defined as the smallest area added to a defined surface generating a surface similar to it.
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**The continuous addition of squares to a golden rectangle generates the spiral arrangement of self-similar squares and the harmonic spiral.
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**Die diagonal surface in the icosahedron is a harmonic rectangle, in which the harmonic spiral is contained, with its self-similarity so to speak a historic fractal. It is contained in the Metaeder.
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**From my subjective viewpoint, the progressive series and the spiral constitute the "junction" between Euclidean and fractal geometry.
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