The digital storehouse, which comprises words and short phrases as well as a year-by-year count of how often they appear, represents the first time a data set of this magnitude and searching tools are at the disposal of Ph.D.s, middle school students and anyone else who likes to spend time in front of a small screen. It consists of the 500 billion words contained in books published between 1500 and 2008 in English, French, Spanish, German, Chinese and Russian.

The intended audience is scholarly, but a simple online tool allows anyone with a computer to plug in a string of up to five words and see a graph that charts the phrase’s use over time — a diversion that can quickly become as addictive as the habit-forming game Angry Birds."

MP: For example, the graph above (click to enlarge) compares John Maynard Keynes to Milton Friedman from 1940 to 2008, and shows that Keynes had more references in published books than Friedman from the 1940s through the mid-1960s and then Friedman had more book references than Keynes from the 1970s through the 1990s. They've now basically been tied since 2000, with Friedman having a slight lead.