Summer reading and summer not

I don't need to see back-to-school ads or falling leaves to know when summer is ending. I just have to check the sales rank for any of my books that are used as summer-reading selections. As the season dies, everything leaps toward larger numbers by a factor of ten. I guess that's a form of decimation. Or decimultiplication. Though we're still a week or so away from the last-minute panic buys that mark the fianl days of vacation.