The numbers from 100-199 represent the philosophy and psychology. This section includes topics that explain why we act the way we do.  Topics include feelings, perceptions, and friendship.   Dewey Number Recommended Websites 100's   110's   120's   130's   140's   150's Optical Illusions (NEIHS Kids' Pages) ...yes, a fun variety of optical illusions 160's   170's   180's   190's