The Charlotte Mason Digital Collection is now part of a much larger worldwide database (WorldCat). Go to http://worldcat.org
If you are given the following suggestion, select the second option -- Stay on www.worldcat.org .
Begin every search by typing cmdc [in order to restrict your results to the Charlotte Mason Digital Collection].
Let's say your topic is nature study. Choose a simple keyword (e.g. nature). Typing less will give you more results.
If you type "nature" (without the quotation marks) you will get more than 90 results, including records with "nature study," "nature notebooks," "Nature-lore." If you type "nature study" you will get a lot less.