It's beach time, and you've probably already scanned a hundred lists of summer reads. Sadly overlooked is that other crucial literary category: the summer non-read, the book that you pick up, all full of ambition, at the beginning of June and put away, the bookmark now and forever halfway through chapter 1, on Labor Day. The classic of this genre is Stephen Hawking's "A Brief History of Time," widely called "the most unread book of all time."

How can we find today's greatest non-reads? Amazon's "Popular Highlights" feature provides one quick and dirty measure. Every book's Kindle page lists the five passages most highlighted by readers. If every reader is getting to the end, those highlights could be scattered throughout the length of the book. If nobody has made it past the introduction, the popular highlights will be clustered at the beginning.

Thus, the Hawking Index (HI): Take the page numbers of a book's five top highlights, average them, and divide by the number of pages in the whole book. The higher the number, the more of the book we're guessing most people are likely to have read. (Disclaimer: This is not remotely scientific and is for entertainment purposes only!) Here's how some current best sellers and classics weigh in, from highest HI to lowest:

"The Goldfinch" by Donna Tartt: 98.5%

This seems like exactly the kind of long, impressive literary novel that people would carry around ostentatiously for a while and never finish. But it's just the opposite. All five top highlights come from the final 20 pages, where the narrative falls away and Ms. Tartt spells out her themes in a cascade of ringing, straight-out assertions.

"Catching Fire" by Suzanne Collins: 43.4%

Another novel that gets read all the way through. "Because sometimes things happen to people and they're not equipped to deal with them" is the most highlighted sentence in the seven-year history of Kindle, marked by 28,703 readers. Romantic heat in the late going also helps to produce a high score.