Google Ngram Viewer
This google facility is a spin off from the Google Books project, the digitisation of all the books on the planet!
Google Ngram Viewer will display a graph depicting the frequency of the use of terms in a chosen selection of books over a nominated time period. You can compare phrases by putting two or more in the same query.
This is a good example of new research methods arising from the increasing role of all things digital that we mentioned in the introduction to digital habits.
Google provides a good set of notes about the facility and there is also a good resource at Harvard's cultural observatory.
Here is a good example of the kind of analysis that this facility allows.
And a fun talk by two of the folk who helped make it happen.