I also enjoyed The Most Powerful Idea in the World: A Story of Steam, Industry, and Invention, by Willam Rosen. It's the story of the steam engine, but also covers the origins of patent law.
It says how long ago something was said, so you can tell last month
from 2014 without doing the arithmetic. Full and green is recent; it
drains and cools as the date gets older, and empties completely at about
6 years.
6d5 days ago
8mo8 months ago
2yr2 years ago
4yr4 years ago
9yr9 years ago
A striped bar means the date itself is an estimate — the source did
not carry an exact one. An entry with no date at all gets no bar.