Here is an easy technique for finding specialized encyclopedias:
On the Libraries home page at http://www,lib.purdue.edu/, click on the "Books & Media" tab, then below the box, click on the words "Advanced Search."
In Advanced Search:
For a more thorough research:
1. Instead of encyc? do other searches using diction? (for dictionary) or manual or handbook or companion.
2. Use a star to multiply your search terms, all in the same search: histor* searches on all possible endings, such as history, historical, historian, historicity, etc. (This is called truncation.)