Google ngram as a research tool

There is a highly useful Google tool here:
http://ngrams.googlelabs.com/

which allows you to search for a word or phrase through all those books that Google has been scanning and also track the rise and fall of the word or phrase over time. You can select by language and bracket by years. And at the bottom of the graph there is a clickable link to the original books. Naturally I immediately tried 'agriculture','railway' for 1800-1870 and found some useful source documents. Might help you.