The copyright holder of this image hereby irrevocably releases all rights to it, allowing it to be freely reproduced, distributed, transmitted, used, modified, built upon, or otherwise exploited in any way by anyone for any purpose, commercial or non-commercial. However, as a courtesy, a link back to https://books.google.com/ngrams would be appreciated.
"Ngram Viewer graphs and data may be freely used for any purpose, although acknowledgement of Google Books Ngram Viewer as the source, and inclusion of a link to https://books.google.com/ngrams, would be appreciated."