Information is Beautiful's caption: "See how big cocaine was in Victorian times."
This is Google Books' new Ngram Viewer tool. Looks like it gives you the prevalence of your search terms over the years in published books.
So... it's Google Trends for history! That's awesome! I don't know why but I've loved Google Trends ever since it came out. In case you aren't familiar, it shows you how often people search for any set of terms you're interested in. So it's a rough, but surprisingly insightful view of the rise and fall of public interest over time for anything searchable.
I use it all the time, but I'm often disappointed at its historical wall of 2004. It doesn't show data from before then. And in any case Google didn't exist before the late 90's so you're out of luck if you're curious when Aerosmith's comeback really kicked in or when people actually started paying attention to Watergate.
So it's not like the Google Books' new tool has that kind of granularity. But the point is, we finally have a tool for seeing the general rise and fall of concepts in the popular zeitgeist.