In reply to The Penguin Grid:
I think the rectangle is a golden one, and these drawings are how to get what are supposedly--and maybe actually are--good proportions. For more of this stuff read Bringhurst's Elements of Typographic Style, or you can look at Tschichold's stuff on it. There is a long tradition of efforts like this. And those Penguin books were actually well designed. Tschichold and Schmoller were famous for lifting the game of book design in England after the second world war. However, this design was a bit later. Some of its story is here.