Alexis finds it:
Allow me to introduce you to a most excellent time-wasting tool. It's called the Books Ngram Viewer, and it allows you to track the plot of words and phrases through time. The service draws on the absolutely massive Google Books corpus. Google estimates they've scanned and OCR'd more than 10 percent of all the books ever published, and they use ... about a third of the total books in the tool. So, perhaps this isn't a perfect tool for research, but man is it fun to play with.