We obtain a generalization of a property of the arbelos first stated as Proposition 4 in the Book of Lemmas by Archimedes, circa 250 BC. The new theorem relates the areas of a chain of four consecutively tangent circles to the area of a circle orthogonal to, and with a diameter tangent to, two of the original circles. The proof of the theorem uses isotropic projection of the 3-dimensional affine Minkowski space onto an embedded Euclidean plane. Proposition 14 of the Book of Lemmas (the Lemma of the Salinon) is then derived from the generalization.
Mathematics Subject Classification (2000). 51B15, 51B20, 51A15, 51A30, 51M05.