AFTER lunch one summer with my grandmother, years ago at her Connecticut farmhouse, she asked me to retrieve an inconsequential item from a closet in my grandfather’s study, and something else caught my eye. At first it didn’t look like much: a set of three slim ledgers with marbleized covers, perhaps a journal of expenses or a record of household bills. But in it were pages and pages of names, methodically scribed in pen and ink. I had found a roster of my grandfather’s students over the more than 40 years he had taught at Columbia University, each name with a grade meticulously recorded next to it. At the top of each page was the year and course title — “The Narrative Art,” “The Poetry of Thomas Hardy,” “Literature Humanities,” …