Since 2004, Google has digitized more than 15 million books, mostly to build its Google Books service. But yesterday Google Labs released a nice little spinoff product, the Ngram Viewer, that provides a window into how we have historically used words, and what these usages say about our culture.
This new visualization tool lets you map out the usage of a given word, or series of words, over a 200 year period (1800 - 2008). For example, the Ngram Viewer shows us that we think less about "war" these days, as compared to the 1940s and 1960s, and more about "terrorism." (Click the links to "war" and "terrorism" and you will see what I mean.) Similarly, the English speaking world has recently renewed its love affair with the dog vis-a-vis cats. And if you invested in salsa and bailed on ketchup in 1980, you would be a pretty wealthy person right now.
Overall, the Ngram database contains roughly 5.2 million books (a subset of the larger Google Books database), with some 500 billion words, and it features texts in Chinese, English, French, German, Russian, and Spanish. Get more details here.