[chx]

The ratio is much, much larger. Darwin's book is not an easy read but luckily you don't need to read Darwin's book, Almost like a Whale by Steve Jones is an excellent rewrite of it. Chapter by chapter, the same arguments are presented but where Darwin could only guess, Jones could rely on genetics and other advances in sciences.

Newton’s Principia is totally and absolutely impossible to understand to the average curious person raised on Cauchy and Weierstrass. There was a course at university aimed at people with advanced math knowledge to prepare you to read it.