Answer: a tool to help find the periodicals that contain articles on a particular subject.
A periodical index is a tool that contains the subject, author and keywords of a particular list of periodicals. This tool helps you find articles about specific topics. The way to look through an index is similar to that of looking for items in a library catalog.
Both poems ask the subjects (the tiger and the lamb) who created them. Both poems point to a fact that there had to be some higher being that created them so perfectly. Both poems also use repetition in the beginnings and ends. Both poems highlight an importance of believing in Gods and creators.
