Squaring the Circle
Union of Earth and Heaven
Maier took it from the Rosarium philosophorum (1550), where 'Aristotle' squares the circle for the union of king and queen.
Richard J. Oosterhoff, 'Learned Failure and the Untutored Mind: Emblem 21 of Atalanta fugiens', Furnace and Fugue (University of Virginia Press, 2020), citing Rosarium philosophorum (Frankfurt, 1550), fol. [29]v
A square of a circle's area, by compass and straightedge.
More context
Squaring the circle is the classical problem of constructing, with compass and straightedge in finitely many steps, a square equal in area to a given circle. Greek geometers worked at it from the fifth century BCE, and Ferdinand von Lindemann proved it impossible in 1882 by showing that pi is transcendental. In alchemy the figure stood for the making of the stone. Michael Maier's emblem XXI (1617), taken from the Rosarium philosophorum (1550), turns man and woman into circle, quadrangle, triangle and circle again.
Light
Maier's epigram: if the work seems abstruse, 'Geometry will soon inform your mind'.
Shadow
After Lindemann's 1882 proof, circle-squaring became the mark of the amateur crank.