Google Books Ngram Viewer

Graph these comma-separated phrases:
case-insensitive
between and from the corpus with smoothing of .  
Search in Google Books:

1900 - 1926 1927 - 1951 1952 - 1956 1957 - 1997 1998 - 2008 tractor English
1900 - 1908 1909 - 1942 1943 - 1950 1951 - 1989 1990 - 2008 mule English

Run your own experiment! Raw data is available for download here.
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