An n-gram is “a subsequence of n items from a given sequence.” Google has come up with what it calls an Ngram Viewer that allows you to compare the frequencies of words in printed books over any span of time since the invention of printing. (It’s case-sensitive, so you can discover, as Shaun Nichols did, that people stopped capitalizing “Socialism” around 1945.) You can read about it in this SciAm article by Katherine Harmon:
The researchers behind the Books Ngram Viewer admit it will not likely replace tried-and-true techniques of close reading…. Despite the program’s capacity to churn out neatly organized analytics at the click of a button (labeled, cheekily, “search lots of books”), Aiden maintains that “we certainly don’t view this tool as an answer machine.” But certainly the program can work as a question generator.
For example, the evolution of the frequency of “evolution” … reveals some unexpected nuances. It was on a general upswing until the mid-1920s, then declined gradually until around 1945 (from about .0035 percent of words in the measured data that year to about .0025 percent). Why the dip—and is it significant? The researchers were unsure and offer this as an example of a lead in for further research, Michel notes.
The Books Ngram Viewer also can shed some light on the popularity of various people, revealing, for instance, a marked dearth of references to Jewish artist Marc Chagall in books published in Nazi Germany, suggesting widespread censorship, the researchers concluded in their paper. (For those more keen on following scientists, the frequency of “Albert Einstein” mentions surpasses those of “Charles Darwin” in the late 1960s, but both enjoy a rise in popularity from about 1975 to 2005, according to a recent search—and the researchers found that Freud ranks higher over time than Einstein or Darwin.)
The first thing I did with it was to check linguistics versus philology; the graphs cross just before I was born.
Addendum. See Geoff Nunberg’s post at the Log for more detail and some interesting commentary.