Mathetische Farbenlehre
Wilhelm Ostwald's 1918 Mathetische Farbenlehre, published in Leipzig by Unesma, is a German treatise on color theory that sets out its system through geometric diagrams. The four pictures are plain line drawings of circles with lettered points, chords, a triangle and a sector, with black dots marking positions on a colour-circle-like figure, giving a designer a clear model for diagrammatic colour wheels and labelled geometric schemes.
