When you open Gale eBooks, use the "Basic Search" box in the upper left to get the most results.
Some of the encyclopedia searches in Gale eBooks won't have your term in the title of the article, but the term will be addressed within the article itself (trespass to land and contributory negligence are a couple examples) - click on the articles and do CTRL F (or command F if using a Mac) to search the text of the article for your term.