Thomas Schoch [2] tells the remarkable story of his discovery in the 1970’s of
the many Archimedean circles in the arbelos (shoemaker’s knife) that were eventually
recorded in the paper [1]. In this note, we record four more Archimedean
circles which were discovered in the summer of 1998, when the present author took
a geometry course ([3]) with one of the authors of [1].
Consider an arbelos with inner semicircles C1 and C2 of radii a and b, and outer
semicircle C of radius a + b. It is known the Archimedean circles have radius
t = ab
a+b . Let Q1 and Q2 be the “highest” points of C1 and C2 respectively.