Books are indexed in our catalog using Library of Congress subject headings. This is a controlled vocabulary system that allows books on similar topics to be grouped together.
Often, you will find a few more books on your topic simply by going to find ONE book you have the call number for. This is called serendipitous discovery and is why browsing the shelves can be very useful when doing research.
The nature of the internet does not allow for serendipitous searching, so if you have the time, take advantage of browsing the shelves!