The power of form applied to geometric tracery : one hundred designs and their foundations resulting from one diagram (1851)
Billings, Robert William, 1813-1874 · Edinburgh ; London Published by the author by William Blackwood and Sons · leaf 66
It is not the number of different curves used that always produces the best patterns;thus, the principal frame of this pattern is the repetition of the circles 1. … XXXVII.
Decoration and ornament · Geometrical drawing
Internet Archive · Getty Research Institute · Public Domain Mark 1.0. Free to use for anything.