Boswell tells about a visit made by Samuel Johnson and the painter Sir Joshua Reynolds to the home of a new acquaintance. When the two men were taken to a sitting room to wait for their host, Dr. Johnson immediately went to the bookshelf and began perusing the "backs of the books," by which I believe Boswell means what I would call the spines.
I've done this same thing many times at homes and in offices. It seems that checking out the books on the shelf should tell you something about their owner. A lot of books by one author is a very good sign that the owner is a fan. The sight of a lot of paperbacks probably indicates a desire for reading that challenges the bank account. Old editions show an interest in collecting and a respect for tradition. The order or disarray, creases in the spines, protruding bookmarks, "used" stickers, dust jackets or exposed hardback cover -- it's all fascinating and informative. And of course seeing a lot of favorite titles could mean that you've found a new friend.
The books on the shelf might be misleading, though. Books on subjects that might demand belief -- economics, politics, religion, and the like -- might indicate interest without commitment. Some books might have been misguided gifts, never to be enjoyed. I have a few misleading books on my living-room shelves. They're scattered around the shelves in no particular order, and I often wonder what guests think of them, although I know that most guests don't love to look as I do. Mostly they're jammed in tightly on low shelves, a good sign that I have tiny grandkids.
Dr. Johnson didn't claim to look at the books in order to learn more about his host, though. Sir Joshua said that he (Sir Joshua) had an advantage: being immediately drawn to the paintings on the wall, instead, he could see entire artworks at a glance. But he asked Johnson why he only looked at the spines without bothering to look inside. The lexicographer answered that by learning titles, he could at least learn more about where to find certain kinds of information. It occurs to me that I look at the shelves for this reason, too. It's almost impossible for me to look up a book in a library catalog and then go straight to that book on the shelf and grab it without looking at all the other titles around it. And I've learned a lot just glancing through bibliographies. Some titles made it to my ten-year plan for no other reason than that I saw them in a list of books compiled by Mortimer Adler.
The same thing happens when I look through a table of contents. I might have opened the book or journal in order to read one particular article, but I usually end up reading something else that catches my eye, too (or instead). And I've learned a lot of music literature just by going through tables of contents looking for the one short piece I intended to study or practice. I had a very intelligent, very talented blind graduate student once who revealed what I thought was a tragic consequence of his condition. For many great composers, he could name only one piece. His piano teacher had assigned pieces, and he had requested Braille versions of them from the Library of Congress. But he had never had the joy of searching a table of contents slowly.